Pregnancy

Pregnancy Trimesters: What To Expect & Do

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pregnancy trimesters

 

Overview

Wondering what the pregnancy trimesters are and what you should expect for each one? Here’s a handy guide to use throughout your pregnancy

By the end of this article, you’ll know more about these pregnancy trimesters, whether there are foods or activities to avoid, how your baby develops, and tests you might need to undergo for each one.

We’ll also answer the most common questions on which trimesters are the riskiest, hardest, or most painful. You’ll also find ideas on when to start preparing your baby’s nursery, hospital bag, birth plan, and postpartum essentials.

 

Important Pregnancy Terms To Remember

  • Zygote – Fertilized egg (your baby right after fertilization)
  • Embryo – Your baby during early pregnancy (before 10 weeks)
  • Fetus – Your baby starting from week 10 gestation (or 8 weeks after conception)
  • Gestational age (counted in pregnancy weeks starting from the first day of your last menstrual period or LMP)
  • Amniotic fluid – The clear, yellowish liquid that surrounds your baby (embryo or fetus) in your womb
  • Placenta – Special organ formed during pregnancy to provide nourishment and protection for your little one until birth
  • Umbilical cord – The long cord that connects your baby (embryo or fetus) to the placenta to receive much-needed oxygen and nutrients (read about cord blood banking here)
  • Lanugo – Soft, downy hair covering your little one in your womb (this fades away in late pregnancy)

 

Key Points: Important Things To Know About The Pregnancy Trimesters

What Are The 3 Trimesters Of Pregnancy?

A pregnancy is divided into three trimesters: (1)

  • 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)

 

You might notice that the weeks of pregnancy vary slightly for each trimester among different resources, including authoritative sites like: (1)(2)(3)

  • ACOG (the American College of Obstetricians and Gynecologists; acog.org) – First trimester (from week 1 to 13), second trimester (from week 14 to 27), and third trimester (week 28 to 40)
  • NICHD (Eunice Kennedy Shriver National Institute of Child Health & Human Development; nichd.nih.gov) – First trimester (from week 1 to 12), second trimester (from week 13 to 28), and third trimester (week 29 to 40)
  • UNICEF (United Nations International Children’s Emergency Fund; unicef.org) – First trimester (from week 1 to 12), second trimester (from week 13 to 28), and third trimester (week 29 to 40)

 

This is, however, just a slight 1-week difference. While important milestones happen during each week of pregnancy, you don’t have to worry about the slight differences in the counted weeks (depending on which trimester schedule you follow).

For uniformity, we follow ACOG’s schedule in this article.

 

What’s The Longest Trimester?

Based on ACOG’s schedule, the second trimester is the longest because it has 14 weeks compared to 13 each for the first and third trimesters.

However, babies rarely follow their due date. You might give birth earlier or later than the 40-week mark. So, the third trimester can easily be the longest (for births in week 42). (2)

 

Which Trimester Is The Hardest During Pregnancy?

The answer varies for different pregnant women

For example, you might experience a difficult first trimester with morning sickness affecting your daily activities, then have a smooth sailing ride until delivery. 

On the other hand, you might not even notice that you’re pregnant for the first two trimesters, yet be on bed rest in the third trimester over a high-risk pregnancy.

Other moms-to-be might experience the reverse of what you’re going through.

Here are some first-hand experiences from a couple of moms on Reddit: (4)

(source: reddit.com) (4)

 

Which Trimester Is The Most Critical?

Although each pregnancy trimester has varied “critical development periods” for different organs and systems, the first trimester is considered the most critical. This is when most miscarriages occur, or possible birth defects develop. (5)

Organs or systems that haven’t fully developed yet are sensitive to harmful exposures from environmental toxins, drugs and medications (read about Tylenol in pregnancy here), maternal infections or medical conditions, etc. (5)

Thankfully, once a body part has fully formed, it’s less likely to be affected by developmental problems that lead to birth defects. However, your baby’s body parts can still be affected in some way, even in late pregnancy, so it’s still important to be careful. (5)

 

What Is The Riskiest Trimester?

Again, each trimester has its risks, and experiences can vary among pregnant women. However, the first and third trimesters might carry the most risks. 

The first trimester has the highest risks for miscarriages and birth defects. Yet the third trimester also has potential life-threatening risks, such as: (6)(7)(8)

  • Preeclampsia and other hypertensive (high blood pressure) disorders
  • Preterm labor and delivery
  • Bleeding or hemorrhage
  • Stillbirth for various reasons, including due to complications from untreated cholestasis of pregnancy 

 

Preterm labor can still occur in the second trimester, and babies born in this period have a very low chance of survival. (6)

 

What’s The Most Painful Trimester?

It still varies among moms-to-be, but many consider the third trimester to be the most painful due to labor and birthing pains. 

 

What’s The Most Important Pregnancy Week?

Every pregnancy week is important because different organs and body systems develop at different schedules. For example, the lungs are among the last to fully develop and are only considered fully ready at 39 weeks. That’s why your healthcare provider will try to ensure you give birth at full term. (5)

However, because pregnancy can only proceed if the fertilized egg implants, then weeks 3 and 4 can be considered the most important. When a fertilized egg doesn’t implant, your body sheds it with the endometrium during menstruation. (9)

 

Stages Of Fetal Development

  • Zygote (formed from the union of the egg and sperm at fertilization)
  • Blastocyst (ball of cells that rapidly divides and gets ready for implantation during the germination stage)
  • Embryo (up to 9 weeks gestation)
  • Fetus (starting from week 10 gestation or 8 weeks after conception)

 

The Stages Of Pregnancy & How Your Baby Grows

Pregnancy progresses at different rates among pregnant women but typically follows a similar pattern for each gestational week. (10)

For example, your baby might have a slightly different weight or length at a particular time but will likely develop the same minor or major organs as other embryos or fetuses during the same pregnancy week or trimester.

Below are developmental milestones and other things you can expect per pregnancy trimester. You can also read our guide for the 40 pregnancy weeks if you want to know more about your weekly progress.

 

Ovulation, Fertilization, & The First Trimester Of Pregnancy (1-13 Weeks)

Key Points For Early Pregnancy

Your Body Prepares For Fertilization & Pregnancy

Each month, beginning with the onset of puberty, your body prepares for possible fertilization by producing an egg. The lining of your uterus (called the endometrium) also thickens to prepare for implantation. These are shed off via blood during your menstrual period if the egg isn’t fertilized. (9)

 

Conception: How Pregnancy Begins

Once released during ovulation, the egg can be fertilized within 24 hours. Freshly ejaculated sperm can reach the egg within minutes. (9)

However, sperm can survive up to five days in your reproductive tract. So, it’s also possible that one of them will reach the egg first. (11)

 

What Happens After Fertilization

The zygote or fertilized egg will travel to the uterus for implantation. The journey takes about a week. (9)(12)

Many factors make determining the actual date of conception difficult. That’s why doctors use your LMP (last menstrual period) to calculate your EDD (estimated due date).

Once the zygote implants, pregnancy hormones such as the hCG (human chorionic gonadotropin) are activated. The hCG signals your body to keep the endometrium from shedding. This is also the hormone detected in pregnancy tests. (9)(13)

Sometimes, errors in fertilization or implantation occur, resulting in a chemical pregnancy. Even though the egg was fertilized, it failed to implant or was miscarried in early pregnancy. Blood tests might still detect a pregnancy, but the embryo, if there’s any, doesn’t develop into a baby. (14)

You might notice implantation bleeding about two weeks after the actual implantation date.

In rare cases, an ectopic pregnancy happens when the fertilized egg implants along the fallopian tubes instead of your uterus. It can be a dangerous, life-threatening condition that can cause internal bleeding if not discovered before the tubes burst.

 

What’s The Placenta & When Does It Form?

When the fertilized egg forms a blastocyst (ball of cells) upon rapid division, the outer part develops into the placenta. This temporary, pregnancy-specific organ gives your baby the nourishment they need until birth. (13)

It takes weeks for the placenta to develop, gradually forming in the first trimester of pregnancy. Proper placental development is essential in a healthy pregnancy. (15)

Sometimes, genetic errors during fertilization occur, resulting in a molar pregnancy. A placenta still forms but might be abnormal and can’t sustain the embryo’s needs. There are also times when the fertilized egg doesn’t turn into an embryo due to genetic errors. (16)

Proper placental attachment and development are also important. If the placenta develops close to the cervix, it can lead to placenta previa, a dangerous condition that can lead to pregnancy loss. (15)

In extremely rare cases, placental abruption happens. The placenta detaches from the uterus long before childbirth is supposed to happen, leading to a higher risk of stillbirth and even maternal death. This may be due to diabetes, hypertension, drug use, or polyhydramnios (excessive amniotic fluid). (15)

It’s important to undergo regular prenatal care with your OB/GYN or any doctor at a women’s health facility so these potential risks might be discovered sooner rather than later.

 

What Happens To Your Uterus During Pregnancy?

Your uterus is an amazing organ that can expand to accommodate your growing baby. It’s about the size of a grapefruit at around week 12 but can grow into watermelon size or more during the third trimester. (17)

 

Why Does Your Period Stop During Pregnancy?

You get your period monthly each time the egg isn’t fertilized. It’s a way to prepare a fresh endometrium for the next ovulation cycle. However, once pregnant, your body produces hCG hormones to prevent your endometrium from shedding off. It helps you keep your baby. (9)(13)

 

Expectations (First Trimester ): For You

(source: nationalpartnership.org) (17)
(source: nationalpartnership.org) (17)

 

Pregnancy symptoms vary among women and even among your own pregnancies. Here are some common symptoms pregnant women experience in these weeks: (10)(13)

  • Frequent urination
  • Tender breasts
  • Nausea and vomiting (typically associated with morning sickness)
  • Weight gain or loss
  • Headaches
  • Heartburn
  • Leg cramps
  • Lower back and pelvic pain
  • Constipation
  • Sudden cravings for certain foods
  • New dislike of certain foods or scents (even if they were your favorites)
  • Extreme fatigue or bursts of energy

 

Expectations (First Trimester): For Your Baby

Organs that typically begin to develop during this period: (10)(12)

  • Neural tubes
  • Brain
  • Spine and spinal cord
  • Cardiac tissue
  • Blood cells
  • Inner ear
  • Genitals (but they aren’t clear yet on the ultrasound scan)
  • Liver
  • Eyelids
  • Pancreas
  • Kidneys
  • Cartilage for the feet, hands, and limbs
  • Muscles of the eyes, mouth, and nose
  • Webbed fingers and toes
  • Fingernails
  • Lungs

 

By the end of the first trimester, your baby will be around 1 lb heavy and about 4 in (10 cm) long. (10)

 

Possible Tests For Your Prenatal Visit

Some tests your doctor might recommend during the first trimester: (18)(19)

  • Pregnancy test (home pregnancy test kit or blood test)
  • First-trimester screening test, includes an ultrasound test for fetal NT (nuchal translucency) for possibly thickening or increased fluid on the fetus’ neck and maternal serum blood tests (hCG and PAPP-A or pregnancy-associated plasma protein-A) to check for abnormal levels that might indicate genetic abnormalities 
  • Cell-free DNA screening test for genetic abnormalities that weren’t found by the multiple marker tests 

 

The ultrasound scan also detects your baby’s heart rate, size, and estimated weight, which can be used to determine their gestational age. (18)(19)

 

What’s The Earliest Week To Do A Pregnancy Test?

If your hCG levels are high enough, a pregnancy test kit can detect them by around week 4 or the same day as your missed period. 

Note that it’s easy to get a false negative result if your hCG levels are still low. 

Using your first-morning urine is ideal because it can contain the highest concentration of hCG. However, some pregnancy test kits are sensitive enough to be used at any time of the day. You can also wait a few more days to repeat the test (around week 5).

 

Are There Foods Or Activities To Avoid?

A healthy and balanced diet is important for a healthy pregnancy. Eat foods rich in iodine, calcium, iron, choline, and EPA and DHA. Talk to your doctor about the right prenatal vitamins (e.g., The Honest Company Love The Bump) to take. 

Avoid eating raw or undercooked meat, meat products, and eggs during pregnancy, especially in the first trimester. They can increase your risks for listeriosis and toxoplasmosis, conditions that can cause: (20)

  • Miscarriage
  • Serious, life-threatening illnesses
  • Severe birth defects 

 

Don’t overexert yourself with strenuous exercises and other extreme physical activities. If possible, talk to your doctor before starting any exercise regimen, especially if you weren’t active before getting pregnant and/or you might have a high-risk pregnancy.

While prenatal yoga can have many benefits (e.g., lowered blood pressure, better sleep, and less low back pain), avoid hot yoga (done in a heated room) or certain pregnancy-unfriendly yoga poses

 

Second Trimester Of Pregnancy (14-27 Weeks)

Expectations (Second Trimester): For You

(source: nationalpartnership.org) (17)

 

Some pregnancy symptoms you might experience during the second trimester: (21)

  • Lower back and pelvic pain
  • Carpal tunnel syndrome (feeling of tingling, numbness, or weakness in your wrist or hand)
  • Linea nigra (a black or dark line that runs from your pubic hairline to your belly button)
  • Darkening areola
  • Patches of darker skin on your face
  • Stretch marks on your tummy, breasts, buttocks, and/or thighs

 

Expectations (Second Trimester): For Your Baby

Some of the new developments your little one will experience during the second trimester: (21)

  • Nervous system begins to develop
  • Brain section that controls motor movements is fully formed
  • Bones start to harden
  • Skin begins to thicken
  • Hearing begins to develop
  • Eyelids can open and close
  • Digestive system begins working
  • Toenails form
  • Kicks are stronger and are now noticeable
  • Genitals are fully formed (detectable on an ultrasound scan)
  • Lungs are fully formed (but still need to fully develop so they can breathe independently)

 

By the end of the second trimester, your baby will be around 2-4 lbs heavy and about 14 in (35 cm) long. (21)

 

Possible Tests For Your Prenatal Visit

Some tests your OB/GYN might recommend during the second trimester, usually around weeks 15 to 20 but ideally by weeks 16 to 18: (19)(22)

  • Multiple-marker second-trimester tests, including hCG levels, hormones inhibin and estriol, and AFP (alpha-fetoprotein) for possible genetic defects, including Down syndrome, chromosomal abnormalities, spina bifida (neural tube defects), abdominal wall defects, or miscalculated due dates
  • Cell-free DNA screening test for genetic abnormalities that weren’t found by the multiple marker tests
  • Glucose screening test for gestational diabetes
  • CVS (chorionic villus sampling) (testing your placenta for possible genetic defects)
  • Amniocentesis (testing your amniotic fluid for spina bifida or chromosome problems)

 

Are There Foods Or Activities To Avoid?

Continue to eat healthy foods and do your doctor-approved, regular exercise routine. Avoid over-exerting yourself with exercise or other physical activities. Slow down if you struggle to catch your breath or converse while doing exercise. (21)

 

Third Trimester Of Pregnancy (28-40 Weeks)

Expectations (Third Trimester): For You

(source: nationalpartnership.org) (17)
(source: nationalpartnership.org) (17)

 

Some pregnancy symptoms you might experience during the third trimester: (23)

  • Shortness of breath
  • Acid reflux (heartburn)
  • Hemorrhoids (swollen, possibly painful veins in your anus)
  • Breast tenderness
  • Protruding belly button
  • Swelling in your face, fingers, and ankles
  • Sleeping difficulties

 

As your baby grows, your uterus also balloons to accommodate their growth. Your baby’s weight and size can affect your movement and give you discomfort. A pregnancy pillow might help support your belly so you can sleep more comfortably.

You might also experience Braxton Hicks or “false labor” (tightening on your abdomen that might feel like menstrual cramps). Call your OB/GNY if the contractions become more intense, frequent, or painful. This might be a sign of early labor. (23)

 

Expectations (Third Trimester): For Your Baby

Developments during the third trimester: (23)

  • Brain, nervous system, and lungs are developed (towards the end of the trimester)
  • Circulatory system is complete
  • Musculoskeletal system is complete
  • Bones harden
  • Eyes can sense light changes
  • Head might already have some hair
  • Lanugo begins to fade
  • Limbs start to look chubby
  • Grasp, kick, and stretch (their kicks feel stronger)
  • Fat continues to develop

 

If they haven’t already, your little one will move to the head-down position during the third trimester in preparation for birth. 

By the end of the third trimester, your baby will be around 6-7 lbs heavy and about 18-20 in (46-51 cm) long. (23)

 

Possible Tests For Your Prenatal Visit

Some tests your OB/GYN might recommend during the third trimester: (19)

  • Fetal monitoring (for fetal heart rate, oxygen, and other functions)
  • GBS (Group B streptococcus bacteria) test; GBS can cause meningitis and pneumonia, so your doctor might recommend antibiotics to reduce your baby’s risks of contracting the bacteria from your birth canal during delivery
  • Genetic carrier testing (for genetic disorders such as sickle cell anemia, thalassemia, Tay-Sachs disease, and spinal muscular dystrophy)

 

Are There Foods Or Activities To Avoid?

Like in previous trimesters, healthy foods and non-strenuous exercise are advised during this last stretch. Again, while walking is ideal, avoiding strenuous activities is best. (23)

A Journal of Education and Health Promotion study (2021) showed that walking during late pregnancy can help: (24)

  • Increase spontaneous labor onset
  • Improve Bishop score (vaginal delivery with induction but similar to spontaneous labor)
  • Decrease risks for induction, cesarean delivery, or instrumental delivery

 

Labor & Delivery

(source: nationalpartnership.org) (17)

 

What’s The Ideal Pregnancy Week To Give Birth?

For scheduled deliveries (such as a C-section or labor induction when there are other pregnancy risks), it’s ideal to still wait until week 39.

Different organs, particularly the brain and lungs, continue to develop until late pregnancy. Studies have also shown that babies born before 39 weeks have a higher risk of hearing and vision problems, developmental delays, and cerebral palsy. (2)

ACOG revised the birth classifications to the following: (2)

  • Preterm or premature birth: From 20 weeks to 37 weeks 
  • Early term birth: From 37 weeks to 38 weeks 6 days
  • Full-term birth: From 39 weeks to 40 weeks 6 days
  • Late-term birth: From 41 weeks to 41 weeks 6 days
  • Post-term birth: From 42+ weeks

 

However, babies don’t usually follow their delivery schedules. Most will come out when they’re ready. If your baby is born prematurely or late (late or post-term), they might need some medical interventions before they can be discharged. (2)

 

Some Resources To Help You With Labor & Delivery Concerns

 

All About Premature Delivery: Health & Medical Concerns

Most premature babies spend some time in the NICU (neonatal intensive care unit) for various medical interventions to increase their survival chances. Your preemie has a higher survival rate if they’re born closer to their due date.

The following are some of the possible complications of a premature birth: (2)(25)

  • Breathing problems
  • Poor health
  • Developmental and/or learning delays 
  • Delayed growth
  • Higher risks of chronic diseases/conditions, including diabetes, hypertension, and/or heart problems later in life
  • Higher risks of visual hearing impairments
  • Higher risks of learning or mental disabilities, ADHD (Attention Deficit-Hyperactivity Disorder), and/or cerebral palsy
  • Higher risk of experiencing SIDS (Sudden Infant Death Syndrome)

 

When Is A Birth Considered Full Term?

A full-term pregnancy or birth ends when you deliver your baby anytime from 39 weeks to 40 weeks 6 days gestation (counting from the last menstrual period).

 

All About Late & Post-Term Delivery: Health & Medical Concerns

Although premature births have higher risks, late and post-term births can also lead to complications, including the following: (15)(26)

  • Placenta problems (including placental abruption)
  • Stillbirth
  • Newborn death
  • No weight gain or even possible weight decrease
  • Meconium (your baby’s first stool) inhalation
  • Decreased amniotic fluid (especially if the amniotic sac was ruptured but the baby wasn’t delivered)
  • Birth injury to you and your baby (such as excessive vaginal tearing because your baby is too large or bruises when forceps are used for delivery)
  • Hypoglycemia (low blood sugar) because your newborn doesn’t have enough stored glucose
  • Longer labor
  • Higher incidence of C-section and its accompanying risks

 

The Postpartum Period: The ‘Fourth Trimester’ Of Pregnancy

Healthcare professionals call the first 12 weeks postpartum (after delivery) the ‘fourth trimester.’ Although you’re no longer pregnant, you still face certain risks. (27)

The postpartum period is considered a ‘critical window’ for women’s health, especially for matters that involve your heart (cardiovascular health), weight, and mental health concerns.

Labor and childbirth can be painful and tiresome, especially because they can last for several hours (some even have labor for days). So, you can expect the following for the next few days after delivery: (28)

  • Fatigue or exhaustion
  • High blood pressure (can also be due to the excitement and/or pain of labor and childbirth)
  • Slightly elevated temperature of around 99°F (37.2°C)
  • Gradual decrease in respiratory and heart rates
  • Weight loss of around 11-13.2 lbs (5-6 kg) from the expulsion of gestation products (i.e., your baby, the placenta, amniotic fluid, etc.) and blood
  • Uterine contractions (expel the placenta or other pregnancy materials and help the uterus gradually return to its pre-pregnancy size)
  • Tender breasts and the start of milk production for breastfeeding

 

Call your doctor if you feel feverish or have a temperature higher than 100°F (37.8°C). This can be a sign of an infection or other problems. (28)

You should also call your doctor if you experience heavy bleeding, especially when you pass large clots. This may be a sign of postpartum hemorrhage, a life-threatening situation. (28)

Don’t worry if you’re having trouble breastfeeding your baby, especially if you’re a first-time mom. It can take time for your body to produce milk and for your baby to learn how to latch properly. Some moms find a breastfeeding pillow, breast pump, and nipple cream useful.

Learn more from our postpartum recovery timeline and guide.

 

Other Postpartum Concerns

 

Getting Help

When Should You Go To An OB/GYN?

  • As soon as you learn you’re pregnant, such as a positive test kit result after a missed period
  • When you experience pregnancy symptoms, such as morning sickness (e.g., nausea and vomiting)
  • Menstrual period that’s heavier than usual (this can be a sign of an early miscarriage from a chemical or molar pregnancy)

 

Prenatal Care (During Pregnancy)

  • Always follow your OB/GYN’s instructions and schedules on when to undergo pregnancy screenings, prenatal check-ups, and other concerns (e.g., taking prenatal vitamins, etc.)

 

Labor & Delivery Schedules & Concerns

  • Call your doctor once you experience contractions and wait for their instructions on when to go to the hospital
  • Immediately go to the hospital if you experience bleeding, fever, or if your water breaks even if it’s not yet your due date

 

Postpartum Concerns & Problems

  • Call your doctor if you have a fever, prolonged heavy bleeding, or other concerns (even if it’s just a feeling that something isn’t right)
  • Seek help if you’re having suicidal thoughts, feeling sad or angry for no reason, or other possible mental health concerns

 

Calculating Your Pregnancy Duration Or EED (Estimated Due Date)

How Long Will Your Pregnancy Last In Weeks Or Months?

Pregnancy due dates are usually calculated at 40 weeks. Although this roughly translates to 10 months (at 4 weeks per month), pregnancies are considered 9 months. Like regular calendar months, some pregnancy months have 4 or 5 weeks.

 

What’s Your Baby’s Due Date & Will You Actually Give Birth Then?

Using Your LMP (Last Menstrual Period)

There are two ways to estimate your due date using your LMP

The first is to add 280 days or 40 weeks to your LMP date.

Another way to use the following calculation: (29)

  1. Count back three months from the first day of your LMP.
  2. Add 1 year and 7 days from that date.

 

Using Ultrasound Scan

An ultrasound scan can also predict your gestational age and due date based on your baby’s size and development. This can also come in handy when you’re unsure about your LMP. (30)

 

How Do You Know How Many Weeks Of Pregnancy You’re Already In?

  • Count how many weeks it has been since your LMP
  • Get an ultrasound scan

 

Preparing For Your Baby’s Birth

Here are some ideas on when to start preparing for the following:

  • Baby’s nursery: Starting from the second trimester or after the gender reveal (if you want a gender-based nursery)
  • Hospital bag: Start ticking off your checklist during the second trimester
  • Postpartum essentials: Begin collecting or buying the items you need during the late second or early third trimester
  • Baby names: Anytime throughout your pregnancy, but especially in the third trimester
  • Labor and delivery: Learn and practice breathing and pain-management techniques during the third trimester

 

References

(1) https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy

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

(3) https://www.unicef.org/parenting/pregnancy-milestones

(4) https://www.reddit.com/r/BabyBumps/comments/14vdg9f/which_trimester_was_the_hardest_and_most/

(5) Mother To Baby | Fact Sheets [Internet]. Brentwood (TN): Organization of Teratology Information Specialists (OTIS); 1994-. Critical Periods of Development. 2023 Feb.

(6) https://pubmed.ncbi.nlm.nih.gov/22309584/

(7) https://medilib.ir/uptodate/show/3560

(8) Suman V, Luther EE. Preterm Labor. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan.

(9) https://www.peacehealth.org/medical-topics/id/tw9234

(10) https://www.unicef.org/parenting/pregnancy-milestones/first-trimester

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

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

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

(14) https://www.researchgate.net/publication/339282838_The_Chemical_Pregnancy

(15) Herrick EJ, Bordoni B. Embryology, Placenta. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan.

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

(17) https://nationalpartnership.org/childbirthconnection/healthy-pregnancy/your-body-throughout-pregnancy/

(18) https://www.chop.edu/conditions-diseases/first-trimester-screening

(19) https://www.nationwidechildrens.org/family-resources-education/family-resources-library/common-tests-during-pregnancy

(20) https://news.sanfordhealth.org/womens/dos-and-donts-during-first-trimester-pregnancy/

(21) https://www.unicef.org/parenting/pregnancy-milestones/second-trimester

(22) https://www.mountsinai.org/health-library/tests/glucose-screening-tests-during-pregnancy

(23) https://www.unicef.org/parenting/pregnancy-milestones/third-trimester

(24) Shojaei B, Loripoor M, Sheikhfathollahi M, Aminzadeh F. The effect of walking during late pregnancy on the outcomes of labor and delivery: A randomized clinical trial. J Educ Health Promot. 2021 Jul 30;10:277. doi: 10.4103/jehp.jehp_1437_20. PMID: 34485574; PMCID: PMC8395880.

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

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

(27) Choi E, Kazzi B, Varma B, Ortengren AR, Minhas AS, Vaught AJ, Bennett WL, Lewey J, Michos ED. The Fourth Trimester: a Time for Enhancing Transitions in Cardiovascular Care. Curr Cardiovasc Risk Rep. 2022;16(12):219-229. doi: 10.1007/s12170-022-00706-x. Epub 2022 Sep 21. PMID: 36159207; PMCID: PMC9490714.

(28) Chauhan G, Tadi P. Physiology, Postpartum Changes. [Updated 2022 Nov 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan.

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

(30) InformedHealth.org [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Birth: Learn More – When your baby’s due date has passed. [Updated 2022 Oct 20]. 

 

 

 

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