Pregnancy

How Many Weeks Is A Pregnancy & How Often Do Babies Really Follow Their Due Dates?

Updated on
how many weeks is a pregnancy

 

Overview

The human gestation period is usually up to around 40 weeks. Babies born prematurely (before week 37) have a higher risk of health problems – and those born too early have lesser chances of survival. (1)

But one premature baby, Curtis Zy-Keith Means, defied the odds after surviving birth at just 21 weeks and 1 day (148 days). He was born in July 2020 in Alabama, USA. (2)

Baby Curtis was so premature that the NICU medical staff initially told his mom, Michelle “Chelly” Butler, that ‘they don’t keep babies that young.’ She told Guinness World Records that it was very stressful, but her baby showed a strong fighting spirit. (2)

Although he needed round-the-clock care and monitoring, Baby Curtis responded so well that even the doctors were impressed. Neonatologist Dr. Brian Sims explained that Baby Curtis had less than a 1% chance of survival – but he lived. Nine months later, Baby Curtis was discharged from the hospital. (2)

Still, Baby Curtis’ case is extremely rare. In many cases, very premature babies don’t survive. 

So, when’s the ideal pregnancy week to give birth? What’s the most important week for fetal development, and how can you calculate your baby’s due date? Is there a way to know how many weeks pregnant you are without going to the doctor?

You might also be surprised to learn that while premature babies have lower chances of survival, post-term babies can encounter problems, too.

We’ll discuss all of this in detail below, and provide a guide for each pregnancy week.

 

What’s The Most Important Week For Fetal Development?

Every single week is important in fetal development because different body parts or systems grow and progress each week. However, it can also be argued that weeks 3-4 are the most important because implantation happens then. (1)(3)

A baby is conceived with the union of the egg and sperm at around week 2. However, the pregnancy will only progress if the fertilized egg implants in the uterus. Your body, then, begins to provide the embryo nourishment via the placenta. (1)(3)

Also, during this “all or nothing period,” the fertilized egg divides rapidly to form the embryo. Exposure to very harmful factors, such as toxic chemicals, drugs, or radiation, can affect embryo development and lead to birth defects. (3)

As mentioned, every week is considered a “critical development period” for a certain body part or system. Often, body parts that aren’t fully developed before that week can be at risk for developmental problems, including birth defects. (see chart below) (3)

Note that the chart below is in fetal weeks (counted from the first day of conception), while pregnancy weeks (or gestational weeks) are counted from the day of the last menstrual period. For weeks listed on the chart, just add 2 weeks to get the gestational or pregnancy week. For example, the brain and spinal cord begin to develop and are most sensitive starting at 3 fetal weeks (5 pregnancy weeks).

(source: ncbi.nlm.nih.gov) (3)

 

By around 12 fetal weeks (14 pregnancy weeks), your little one’s limbs and major organs have formed, including the heart and brain. (3)

However, it’s still important to keep your baby safe from harmful exposures of any kind, even if they’re still in the womb. Although these exposures are less likely to cause major birth defects in the second and third trimesters, they can still affect your child’s central nervous system. (3)

The brain continues to develop throughout your pregnancy and even after birth up to young adulthood. Developmental problems that affect the brain and nervous system, no matter which pregnancy week they happen in, can lead to learning problems, cerebral palsy, and other conditions. They might even lead to pregnancy complications, including stillbirth and preterm delivery. (1)(3)

Note: For uniformity, all the weeks mentioned below are pregnancy weeks, not fetal weeks.

 

Gestation Length: How Many Weeks Is A Full-Term Pregnancy?

  • 39 to 40 pregnancy weeks (or up to 40 weeks and 6 days)

 

Old Vs. New Definition of “Full Term” Births: Terminologies For Births (By Weeks)

In the past, babies born at 37 weeks (or around 3 weeks from the estimated due date) were considered “full term.” (1)

However, studies have shown that these babies have a higher risk of hearing, vision, and developmental delays, as well as cerebral palsy, than those born at 39 weeks. (1)

So, the American College of Obstetricians and Gynecologists (ACOG) convened and decided on these new classifications based on birth weeks: (1)

  • Preterm Or Premature Birth: 20 weeks to 37 weeks 
  • Early Term Birth: 37 weeks to 38 weeks 6 days
  • Full Term Birth: 39 weeks to 40 weeks 6 days
  • Late Term Birth: 41 weeks to 41 weeks 6 days
  • Post-Term Birth: 42+ weeks

 

Is 36 Weeks Full Term?

No. It’s considered a premature birth. (1)

 

Is 37 Weeks Full Pregnancy?

No. It’s considered an early-term birth. (1)

 

At What Pregnancy Week Is A Baby Born?

Babies don’t follow a specific birth schedule even if doctors estimate their “due date.” Ideally, babies should be born full-term or at least 39 weeks. (1)

 

Why 40 Weeks Is Ideal

Fetal development has schedules for each week of pregnancy. Different body parts, organs, and systems develop at specific times. All these scheduled developments are completed by week 40 – so, it’s ideal for babies to be born at this time. (1)

 

Is Pregnancy 9 Or 10 Months?

Pregnancy is considered as nine months even if 40 weeks is equal to 10 months (based on the calculation: 1 month = 4 weeks). (1)(3)

As you can see on our list of pregnancy progress by week below, some months have four while others have five weeks.

Also, babies don’t follow a specific schedule and aren’t born when they’re 40+ weeks. Instead, many are born before they reach the full term – and that’s within “nine months.” (1)(3)

 

How Many Trimesters Are There In Pregnancy?

There are three trimesters in a human pregnancy: (1)(3)

  • First trimester
  • Second trimester
  • Third trimester

 

How Many Weeks Are There In One Trimester?

There are around 13 or 14 weeks per trimester: (1)(3)

  • First trimester: 13 weeks (from week 1 to 13)
  • Second trimester: 14 weeks (from week 14 to 27)
  • Third trimester: 13 weeks (from week 28 to 40)

 

The third trimester can also extend for 1-2 weeks, depending on your actual delivery date. (1)(3)

 

When Does A Pregnancy Really Start?

Pregnancy officially begins at conception when the sperm fertilizes the egg. However, the exact date of conception is usually unknown. So, doctors estimate the pregnancy based on your last menstrual period (considered week 1). (1)(3)

 

What Are The Stages Of Fetal Development?

  • Zygote (at fertilization)
  • Blastocyst (during the germination stage)
  • Embryo
  • Fetus

 

Let’s discuss these stages below.

 

What Happens At Conception?

Conception happens when a sperm penetrates the egg. This occurs in the fallopian tube. (1)(4)

The conditions have to be right for conception to happen. An egg may only be fertilized up to 24 after ovulation (an egg’s release from the ovary). (4)

Sperm can live up to five days inside the reproductive tract. However, it has to be active enough to swim to and penetrate the egg. (4)

(source: merckmanuals.com) (5)

 

Once the egg is fertilized, the combination is now called a zygote. It travels through the fallopian tube to implant in the uterus. This journey can take about 5-6 days from fertilization. (4)

 

Things To Know About The Germinal Stage (From Zygote To Blastocyst)

The shortest stage of fetal development, the germinal stage, starts with the zygote (fertilized egg). The zygote divides rapidly and becomes the blastocyst. (5)

During this stage, the placenta is formed from the cells on the outer walls of the blastocyst. (5)

Placental development is important because it provides nourishment, protection, and oxygen for your baby throughout the pregnancy. (5)

In rare cases, the placenta fails to develop. Grape-like clusters form in the womb and are unable to nourish the embryo. Sometimes, no embryos form. This is called a molar pregnancy and leads to a miscarriage. (6)

 

Things To Know About The Embryonic Stage

By around 5 weeks gestation (3 weeks after conception), the blastocyst has developed enough to suggest a human shape. This is called an embryo. (5)

The embryo is enclosed in an amniotic sac filled with fluid (called amniotic fluid). (5)

Here’s an illustration of an embryo and the placenta at 8 weeks gestation: (5)

(source: merckmanuals.com) (5)

 

Things To Know About The Fetal Stage

The embryo is considered a fetus by around 10 weeks gestation (8 weeks after conception). Limbs and various structures are now identifiable at this stage. (5)

Continue reading for more details on how your little one develops each pregnancy week. 

 

First Trimester: Pregnancy Milestones By Week

Month One

1 Week

When you get pregnant, the first week of your menstrual cycle is also considered the first week of your pregnancy. While that’s confusing, pregnancy due dates are calculated beginning the first day of your last menstrual period (LMP). (1)(5)

 

2 Weeks

Fertilization or conception usually takes place around about 2 weeks after your LMP. (5)

It’s difficult to tell the exact day you get pregnant. That’s why your health care provider or pregnancy calculators use the LMP to determine your pregnancy week. (5)

 

3 Weeks

The fertilized egg (zygote) takes about a week to travel through your fallopian tubes down to your uterus. Along the way, the zygote rapidly divides and becomes a blastocyst (ball of cells). (5)

Around week 3, the blastocyst attaches to the uterine wall (lining of your uterus) in a process called implantation. (5)

The placenta forms once the blastocyst implants. It comes from the outer cells of the blastocyst. (5)

If two eggs are fertilized simultaneously, they will follow a similar schedule, but your babies will have different genetic material. They’re fraternal twins. (5)

Sometimes, a blastocyst divides to form two embryos. This results in identical twins with the same genetic material because they came from the same fertilized egg. They’re also called monozygotic twins. (5)

The likelihood of having identical twins is rare at 3-4 per 1,000 births. (13)

Surprisingly, while twins from assisted reproductive technology such as IVF (in vitro fertilization) are usually fraternal (dizygotic), the likelihood of identical twins is 2-12x the rate with natural conception. (14)

An IUI (intrauterine insemination) procedure itself doesn’t affect your chances of having twins. However, the rate can increase if fertility medicines are used with the procedure. (15)

Twins or other multiples also implant at around the same time. (5)

In rare cases, the zygote implants in the fallopian tube, leading to a dangerous condition called ectopic pregnancy. Because the tube isn’t designed for accommodating a growing embryo, it can rupture and lead to internal bleeding.

 

4 Weeks

The blastocyst continues to develop and elongate. (5)

Your baby measures about 1/100 of an inch at week 4 and is about the size of a poppy seed. (7)(16)

 

Month Two

5 Weeks 

By 5 weeks, most organs are already starting to form, and the embryo also begins to take a human shape. (5)(8)

Organs that form and begin to develop during this period: (5)(8)

  • Neural tube (this becomes your baby’s brain, backbone, and spinal cord
  • Lungs
  • Heart (your baby’s heart also starts to beat, and the first red blood cells appear during this period)
  • Major blood vessels
  • Tiny limb buds (these become your baby’s limbs)

 

Your baby’s blood vessels, brain, and spinal cord continue developing throughout pregnancy. (5)

They’re about the size of an apple seed. (16)

 

6 Weeks

Organs and body parts that form around this time: (7)(8)

  • Ears
  • Nose
  • Mouth
  • Fingers and toes
  • Tissues that become bones, especially the vertebrae (bones that protect the spinal cord)

 

Your baby (or babies) measures around ⅙ of an inch at week 4. (7) 

Rudimentary (early stage) blood begins to circulate through their nerves. It’s pumped by the heart, which can start beating at a regular rhythm(7)(8)

Their brain will also begin to develop into five areas. (7)

They’re about the size of a sweet pea. (16)

 

7 Weeks

Your baby’s bones start to form, but they’re still soft. They will gradually harden over the course of your pregnancy. 

Genitals also begin to form but are not yet well defined. (8)

They’re about the size of a blueberry. (16) 

 

8 Weeks

The placenta creates villi (hair-like projections) that extend into the uterine wall. Blood vessels develop in the villi and connect the embryo to the placenta through the umbilical cord. (5)

A thin membrane forms to separate the embryo’s blood from your blood. This prevents your body’s immune system from accidentally attacking the embryo (identified as a “foreign substance”). Yet the membrane also allows the exchange of materials (such as nutrients) between you and the embryo. (5)

Your baby’s major organs and systems continue to develop. They now have a 4-chambered heart and nostrils. (5)(7)

Organs and body parts that form during this period: (7)

  • Lungs
  • Toes and fingers (still webbed but more defined)

 

Your baby’s eyes and a shell-like structure for the ears are now visible. (7)

While your baby still looks curled up, their trunk begins to straighten during this week. (7)

Your baby at week 8 is about the size of a raspberry or kidney bean. (8)(16)

 

Month Three

9 Weeks 

Some milestones for this week: (8)

  • Tiny buds that will become your baby’s teeth begin to appear.
  • Hands and feet are developing.

 

Your baby is about ½ an inch long now and is about the size of a grape. (8)(16)

 

10 Weeks

All your baby’s major body parts (e.g., ears, eyes, legs, and arms) have formed and are distinguishable. However, they might still be positioned in other areas. (7)

Eyelids begin to form and protect your baby’s developing eyes. Their nostrils and upper lip also begin to develop. (7)(8)

Toes and fingers continue to develop and are better defined, and their nails start to grow. (8)

You might already hear your baby’s heartbeat when you go for a prenatal care checkup. However, don’t be surprised that it beats fast – at 2-3 times your own heart rate or at 180 beats per minute. (7)(8)

Their elbows might already bend at this point, which might be visible in your ultrasound scan. (8)

Your little one is about 1¼ inch long by week 10 and about the size of a small tangerine. (7)(16) 

 

11 Weeks

 

Your baby’s bones are getting hard – and those on their face are already formed. (8)

Their eyelids stay shut, but their ears begin to take shape on the sides of their head. (8)

At 11 weeks, your baby’s head is larger than their body and can take up as much as a third of their entire length. That’s normal. (8)

Their fingers and toes also begin to separate from their webbed appearance in previous weeks. (8)

They’re about the size of a fig. (16)

 

12 Weeks

Nearly all organs are formed by 12 weeks gestation, except the brain and the spinal cord. (5)

The fetus has grown enough to fill your entire uterus. (5)

Your baby has already begun to move around but is so tiny that you aren’t likely to feel these movements yet. (7) 

Their heartbeat can already be detected electronically, and their face already takes a human form. (7) 

Their genitals are also well-formed by this week but not yet visible on the ultrasound scan. (8)

Your baby’s skeleton has also developed, but it’s still made of soft cartilage, not hard bones. (8)

Your little one is about 2½ inches long, the size of a lime,  and weighs around ½ oz by week 12. (7)(8)(16)

 

13 Weeks

Genitals continue to develop, but you might need another week before an ultrasound scan can detect your baby’s gender. (8)

Other milestones at this week: (8)

  • Digestive system moves to its permanent location inside the body (it was developing outside in previous weeks)
  • Bones on the arms and legs begin to harden

 

Your baby is the size of a peach or about the length of a pea pod at this point. (8)(16)

 

Second Trimester: Pregnancy Milestones By Week

Month Four

14 Weeks 

Sex organs can already be identified through an ultrasound scan by week 14. However, your OB/GYN might want to hold off until week 18. (1)(5)

Some milestones for this week: (7) 

  • The bone marrow begins to produce blood
  • The kidneys make urine
  • Taste buds develop
  • Fetus starts to swallow
  • Eyes start to move
  • Nose develops
  • Hair follicles start to grow under the skin
  • Skin begins to thicken

 

They’re about the size of a big lemon. (16)

 

15 Weeks

Your baby can now hear. The sounds may be muted, but they will likely hear your voice and heartbeat. (8)

Their bones are also growing stronger and may already start getting visible in an ultrasound scan. (8)

Although their eyes are closed, they can already be sensitive to light even if they’re still in your womb. (8)

They’re about the size of a small pear or an apple. (16)

 

16 Weeks

By this week, your baby has grown and become active enough that you might already begin to feel their movements. These movements can be subtle and not easily identifiable. (5)

Women who’ve been pregnant before might feel these movements about two weeks earlier than first-time moms. (5)

Your baby’s upper lip, eyelids, and ears have fully developed. They have also developed their facial muscles and might already start practicing making faces or other facial expressions. (8)

Your little one is about 5 inches long and weighs about 5 oz, and their hands can already reach each other. (8)

Their lungs have also developed to the point where they’re practicing to breathe via the amniotic fluid. (8)

They’re about the size of an avocado. 16)

 

17 Weeks

Progress for this week: (8)

  • Eyelashes and eyebrows grow
  • Eyes can move (the eyelids remain closed)
  • Their face looks more human
  • Fingerprints begin to develop
  • Toenails and fingernails grow
  • Vernix (waterproof, waxy coating) appears on their skin and protects them in your womb

 

They’re the size of a pear. (16)

 

Month Five

18 Weeks 

The placenta is fully formed by this time but continues to grow throughout your pregnancy. (3)(5)

Most would-be moms wait until 18 weeks (or month 5) for the ultrasound scan to determine the baby’s gender. (1)

This is also the week for ultrasound scans to check for possible birth defects. (1)

The ultrasound procedure is your first time to “see” your baby. However, be sure to tell your doctor (or ultrasound technician) if you want to keep your baby’s gender a secret. They can put the gender on their report so you can take this to the baker or someone in charge of the gender reveal if you’re doing one. 

By week 18, your baby’s skin has lanugo (soft, fine hair). (8)

They’re about the size of a sweet potato. (16)

 

19 Weeks

Your baby’s movements and kicks are getting stronger, so you might already feel them this week (if you haven’t previously). They might even respond to music, loud noises, or conversations. (8)

They might already start sucking their thumb in your womb. This prepares them for suckling milk when they’re born. (8)

They’re about the size of a mango. (16)

 

20 Weeks

Many moms begin to feel movement at this period, but some might as early as 16 weeks. (1)

Sweat glands begin to form under their skin, and your little one will now be around 10 inches long and weigh around 1 lb. (8)

They’ll also begin to have sleep and wake cycles. (8)

They’re about the size of a banana now. (16)

 

21 Weeks

Your little one can swallow now and might even hiccup. Their entire body is covered in lanugo. (8)

During this week, they would have already grown bigger than the placenta. (8)

They’re about the size of a carrot. (16)

 

22 Weeks

Your baby continues to develop a sleep pattern, but it might differ from yours. They might be fully awake (possibly kicking hard or moving around) when you’re asleep (or trying to). (8)

They’re about the size of a small squash. (16)

 

Month Six

23 Weeks

Your baby’s lungs continue to develop. Although they aren’t yet working properly enough for your baby to survive without medical assistance at this point, the lungs are already practicing proper breathing movements. (8)

They’re now the size of a grapefruit. (16)

 

24 Weeks

The fetus continues to develop but already has a chance to survive (with close medical supervision) if born during this week. (5)

Your baby’s fingerprints and footprints form by week 24. (1)

Their muscles continue to develop, and they might begin to grow hair. (8)

The lungs are fully formed but will still continue to develop. If born prematurely this week, your baby has a better chance of survival than previous weeks, but will need help breathing. (8)

They’re about the size of a corn ear. (16)

 

25 Weeks

Your baby’s nervous system (brain, spinal cord, and nerves) is developing fast. This helps with movement and thinking. (8)

Your little one may also respond to sounds with movement (e.g., kicking). (8)

Their bodies already produce urine, and they may start peeing in their amniotic fluid. This is filtered out as waste material. (8)

Their eyelids also begin to open, and they start blinking. (8)

Heart rates begin to slow to around 140 beats per minute. (8)

They’re around the size of an acorn squash. (16)

 

26 Weeks

Your baby’s body creates melanin (responsible for skin color; also protects the skin from the sun after birth). Their lungs also begin to make surfactant (a substance that helps their lungs get ready to breathe). (8)

Their digestive system, lungs, and brain are already in their right places (compared to early pregnancy) but are still developing. (8)

They’re around the size of kale. (16)

 

27 Weeks

Your baby will likely do a lot of kicking, stretching, or other movements. Their nervous system and lungs continue to develop, but they’re around 2.2 lbs now. (8)

Their heartbeat might already be strong enough to be heard on a stethoscope. (8)

They’re around the size of a cauliflower. (16)

 

Third Trimester: Pregnancy Milestones By Week

Month Seven

28 Weeks

Babies have a higher survival rate of 92% by 28 weeks than if born younger. However, babies born this young can experience serious health complications, such as neurologic or respiratory problems. (1)

Your baby is about 2½ lbs, around 14 inches long, and about as big as a large eggplant. The protective vernix slowly begins to disappear. (8)(16)

 

29 Weeks

Your baby begins to grow fast and can gain around half their birth weight in the last 2½ months of pregnancy. Their skin can still be wrinkly, but they will fill out at birth. (8)

They’re about the size of a butternut squash. (16)

 

30 Weeks

Your baby begins to lose the soft, fine hair covering their body (the lanugo). Their eyes also begin to focus, but their lungs are still developing. (8)

They’re about the size of a large cabbage. (16)

 

31 Weeks

Your baby’s brain develops rapidly and can help control their body heat. If born prematurely at 31 weeks, your baby still needs help breathing but already has a better chance of survival (about 90%). (8)

They’re about the size of a large coconut. (16)

 

Month Eight

32 Weeks

Milestones for the week: (1)(8)

  • Eyes can now close and open
  • Bones have already formed but are still soft
  • Esophagus (food pipe) already starts to work

 

Your baby might be about 5 lbs, around 18 inches long, and around the size of a Chinese cabbage. They might already turn into the upside-down, birthing position. But if they haven’t, that’s fine. There’s still time before their due date is up. (8)(16)

 

33 Weeks

Your baby grows rapidly as they get closer to their due date, gaining about ½ lb per week. They remain curled up in your womb but can still kick around whenever they want to. (8)

Their taste buds are fully developed at 33 weeks, which might affect their taste preferences even in your womb. (8)

They’re about the size of a pineapple. (16)

 

34 Weeks

The vernix starts to get thicker. Your baby may also move to the head-down position (if they haven’t already) to prepare for birth. If your baby is a boy, their testicles will move toward their proper position from the abdomen to the scrotum. (8)

They’re about the size of a melon. (16)

 

35 Weeks

Your baby’s brain and lungs continue to develop. (8)

They’re about the size of a honeydew melon. (16)

 

Month Nine

36 Weeks 

Babies born at 36 weeks are still considered premature, although they’re already classified as late preterm birth. They still have risks of various developmental, hearing, or vision problems. (1)

However, their lungs can already take in oxygen if they’re born this early. They’re now adept at making surfactants to keep the air sacs open. (8)

Your baby might weigh around 6-7 lbs, and their digestive system can already process breast milk if needed. They’re about the size of a Romaine lettuce. (8)(16)

 

37 Weeks

Important organs, including your baby’s brain, liver, and lungs, are still developing, but they have a higher survival rate than younger babies. (1)

You might expect labor anytime soon if you’ve had a healthy pregnancy. If you need to schedule a C-section, it’s usually done after 39 weeks, except for medical reasons. (8)

They’re about the size of a Swiss chard. (16)

 

38 Weeks

Babies born at 38 weeks have a higher survival rate than preterm ones. However, they’re considered early term and can still have some health risks compared to those born at full term (39-40 weeks). (1)

Your baby’s brain, lungs, and liver continue to develop, but their heart and circulatory system are already fully formed and functioning. (8)

They’re about the size of a rhubarb stalk. (16)

 

39 Weeks

Your baby’s brain, liver, and lungs have fully developed by 39 weeks. They’re full term and ready for birth, so you can expect to experience labor anytime soon (if you haven’t given birth yet). (1)

They’re about the size of a small watermelon. (16)

 

40 Weeks

Your baby’s organs and systems are fully developed. They’re ready to be born (if they haven’t come out yet). However, even during this week, their brain continues developing and producing new cells. (5)

Amazingly, the brain continues developing within your baby’s first year of life and even up to adulthood. (3)(5)

Babies who make it this far usually weigh about 6-9 lbs and can be around 18-20 inches long. They’re about the size of a regular watermelon. The lanugo is also nearly gone by 40 weeks. (8)(16)

 

How To Calculate Your Baby’s Due Date

Why Use LMP (Last Menstrual Period) For Counting Your Baby’s Due Date

You can download a due date calculator app. However, you can also easily count your baby’s due date using your LMP (last menstrual period) as a guide.

To get your due date, just add 40 weeks or 280 days to your LMP date.

Another way to calculate your due date: (9)

  1. Try to remember the date of the first day of your LMP.
  2. Count back three months from that date.
  3. Add one year and seven days from that date. That’s your baby’s estimated due date.

 

Here’s a guide from Johns Hopkins Medicine: (9)

(source: hopkinsmedicine.org) (9)

 

Using Ultrasound To Estimate Your Baby’s Gestation & Due Date

An ultrasound scan can also help your OB/GYN determine your baby’s gestational age and due date. They base this on your baby’s progress, such as their size or other developmental milestones. (1)(5)

 

Other Uses For Ultrasound Technology

Ultrasound is also used to check for your baby’s gender and possible birth defects (including missing limbs or certain abnormalities). (1)(5)

 

Using Conception Date For Counting Your Baby’s Due Date

If you’re sure about the conception date, particularly if you had a fertility procedure such as IVF or IUI, you can add 266 days to that date to get your due date.

 

How To Calculate Your Baby’s Gestational Age (By Week)

As explained above, doctors consider your LMP as the first day of pregnancy, even if your baby is unlikely to be conceived then.

 

Simply count the weeks from your LMP to get your baby’s gestational age.

 

How To Calculate Your Baby’s Gestation Age (By Month)

Again, you simply count your baby’s gestational age from your LMP

 

Counting Pregnancy Weeks & Due Dates With IVF Or Other Fertility Procedures

Transfer dates can be the basis for your due date when undergoing fertility procedures. Add 266 days to your conception/implantation date to get your due date.  Check with your doctor if in doubt, and they’ll let you know your due date.

 

Which Method Should YouChoose For Counting Your Pregnancy Weeks?

It depends on your preferences. But to avoid confusion, consider following the counting for gestational age because this is also what your doctor will likely use. It’s also the basis for many pregnancy guides, including the one we’ve detailed above.

 

Will You Give Birth On Your Baby’s Actual Due Date?

Probably not. Due dates are just an estimate of when your baby will arrive. Most babies are born a few days before or after their due date

 

Preterm Births & The Importance Of Reaching Full Term

Every Single Week Counts

There’s a development schedule for each week of pregnancy, so each one counts. Although babies have a higher survival chance when born in the third trimester of pregnancy, they can also face health risks if not born at full term. (1)(5)

 

Risks Of Preterm Births

The risks can vary, depending on when your preterm baby is born. The younger your baby, the higher the risks. (1)(5)

Possible risks include: (10)

  • Developmental and learning delays (because the brain is among the last organs to develop and mature fully)
  • Poor health
  • Delayed growth
  • Breathing problems
  • Higher risks of chronic conditions/diseases, such as diabetes, hypertension, and heart problems later in life
  • Higher risks of hearing or visual impairments, learning or mental disabilities, cerebral palsy, and ADHD (Attention Deficit-Hyperactivity Disorder)
  • Higher risk of passing from Sudden Infant Death Syndrome (SIDS)

 

Most premature babies spend time in the NICU, although they have a higher survival rate the closer they’re born to their due date.

 

Causes Of Preterm Births

Many factors can lead to preterm births, including: (11)

  • Infections (e.g., urinary tract infections, sexually transmitted diseases, or vaginal infections, such as trichomoniasis or bacterial vaginosis)
  • High blood pressure
  • Vaginal bleeding due to various reasons
  • Certain developmental anomalies in the fetus
  • Blood clotting problems
  • Diabetes (high blood sugar)
  • Gestational diabetes (a diabetes type that occurs only during pregnancy)
  • Your weight before your pregnancy (being underweight or obese) 
  • Placenta previa (when the placenta grows in the lowest section of your uterus, possibly covering all or part of the cervical opening)
  • Risk for uterine rupture of the uterus (the wall of the uterus rips open); increased risks for those who’ve had a previous C-section or surgery (e.g., uterine fibroid removal, etc.)
  • Short time intervals between pregnancies (e.g., less than 6 months between your last birth and the start of the next pregnancy)
  • Pregnancy from in vitro fertilization
  • Nutrient deficiencies (e.g., iron deficiency leading to anemia, iodine, choline, etc.)
  • Maternal age (older moms 35+ years old have a higher risk of preterm birth)

 

Reducing The Risks Of Preterm Births

  • Lifestyle changes (e.g., reduce coffee consumption, avoid alcohol and smoking, stop using illegal drugs and certain medications, etc.)
  • Do your best to manage stress
  • Taking prenatal vitamins (e.g., Honest Company Love the Bump)
  • Going to regular prenatal checkups
  • Avoid exposure to toxic chemicals and other harmful substances

 

Late & Post Term (Overdue) Births

  • Births at 41+ weeks gestation

 

Risks Of Late & Post Term Births

Possible complications of late and post-term births: (12)

  • Placenta problems
  • Stillbirth or newborn death
  • Decreased amniotic fluid (especially if it ruptured but the baby isn’t delivered)
  • Birth injury to you and your baby(especially with forceps delivery and if your baby is large)
  • The baby might lose or stop gaining weight
  • Baby takes in meconium (the first stool)
  • Hypoglycemia (low blood sugar) because your baby doesn’t have enough glucose stored
  • Longer labor
  • Higher incidence of C-sections and accompanying risks

 

Prenatal Care Throughout Your Pregnancy

What’s The Earliest Pregnancy Week To Know If You’re Pregnant?

You can take a pregnancy test on the first day of your missed period (around 4-5 weeks gestation). However, the pregnancy test kit might still give a false negative. A blood test (done in the lab, not at home) can provide more accurate results, especially in early pregnancy.

 

When Should You Go To Your OB/GYN About Your Pregnancy?

It’s best to visit your OB/GYN when you learn or think you’re pregnant. 

 

Seeking Help For Pregnancy Concerns

Talk to your OB/GYN about pregnancy concerns, such as: 

  • Dealing with pregnancy symptoms (e.g., morning sickness)
  • Possible risks for pregnancy complications and birth defects
  • How pregnancy might affect your job
  • Prenatal vitamins

 

Preparing For Your Baby’s Arrival

 

Postpartum Period Concerns

 

References

(1) https://www.nichd.nih.gov/health/topics/factsheets/pregnancy

(2) https://www.guinnessworldrecords.com/news/2021/11/worlds-most-premature-baby-defies-sub-1-survival-odds-to-break-record-681851

(3) https://www.ncbi.nlm.nih.gov/books/NBK582659/

(4) https://www.ucsfhealth.org/education/conception-how-it-works

(5) https://www.merckmanuals.com/home/women-s-health-issues/normal-pregnancy/stages-of-development-of-the-fetus#Fertilization_v809169

(6) https://www.hmole-chorio.org.uk/patients_info/introduction-to-molar-pregnancy/

(7) https://ldh.la.gov/page/stages-of-fetal-development-first-trimester

(8) https://www2.hse.ie/pregnancy-birth/baby-development-pregnancy-stages/stages/

(9) https://www.hopkinsmedicine.org/health/wellness-and-prevention/calculating-a-due-date

(10) https://ukhealthcare.uky.edu/wellness-community/health-information/short-long-term-effects-preterm-birth

(11) https://www.nichd.nih.gov/health/topics/preterm/conditioninfo/who_risk

(12) https://www.stanfordchildrens.org/en/topic/default?id=post-term-pregnancy-90-P02487

(13) https://medlineplus.gov/genetics/understanding/traits/twins/

(14) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515956/

(15) https://www.mayoclinic.org/tests-procedures/intrauterine-insemination/about/pac-20384722

(16) https://parenting.firstcry.com/articles/baby-size-week-by-week-comparison-with-fruits-and-veggies/

 

 

 

 

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