How Long is Pregnancy? (The Answer May Surprise You!)

How long is pregnancy? Despite what you’ve always heard, it isn’t exactly nine months! Find out what surprising factors can affect the length of pregnancy.

How long is pregnancy? Despite what you’ve always heard, it isn't exactly nine months! Find out what surprising factors can affect the length of pregnancy.

If you just found out you’re pregnant, you probably have a lot of questions. When will those early pregnancy symptoms start? Will I have morning sickness? You may even wonder: How long is pregnancy? (Hint: Despite what you’ve always heard, it’s not exactly nine months!) So let’s start with the basics. Read on to discover:

  • How long pregnancy really is
  • How long each trimester is
  • Plus, why there’s debate over how long the third trimester is

How Long is Pregnancy?

It’s commonly accepted that pregnancy is 40 weeks. But you’re not technically pregnant during the first two weeks of pregnancy. Huh?! 

Your due date is calculated based on your last menstrual period (LMP). Healthcare providers or your midwife use the LMP because the conception date is a little harder to pin down. A woman with a normal period typically ovulates 14 days after her period began. (Use our ovulation calculator to find out your ovulation window.) That’s how those 14 days get included in your pregnancy.

(If you know your due date and want an estimate of when you conceived, use our reverse due date calculator.)

How Long is the First Trimester?

Your first trimester lasts 13 weeks. Here at Mama Natural our week-by-week pregnancy calendar begins at week three and ends at week thirteen for the first trimester. It’s counted from the first day of your LMP and lasts through the end of your 12th week of pregnancy.

What to expect during the first trimester

The first trimester is when your doctor or midwife may perform screening and diagnostic tests. These may include:

  • Beta HcG
  • PAPP-A
  • Nuchal translucency
  • Cell-free DNA screening
  • Chorionic Villus Sampling
  • Rh-Factor Testing

Your doctor or midwife will discuss each test and its purpose, your risks, and any family or genetic history that indicates if and when certain tests are warranted. Some women may choose to have a dating scan, though others may decide to forgo ultrasounds.

What’s going on with baby during the first trimester?

At the end of the first trimester, your baby is about three inches long. Their major organs and body parts have begun forming, as has their nervous system, muscles, and facial features. In the last two to three weeks of the first trimester, fingernails and toenails start forming and baby’s kidneys start working. Grow, baby, grow! 

Pregnancy week by week – 12 weeks pregnant – Mama Natural

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When Does the Second Trimester Start?

How long is the second trimester? It begins at 14 weeks from your LMP and ends at the completion of the 27th week of pregnancy. The second trimester is often called the “honeymoon” trimester, because many expectant mothers experience a relief from morning sickness, your emotions stabilize, and your sex drive comes roaring back. It’s also when you’ll feel baby’s first kick, and can find out the baby’s sex.

What to expect during the second trimester

During the second trimester, your healthcare provider may recommend or want to run the following tests:

  • Triple screen/Quad screen
  • Amniocentesis
  • Anatomy ultrasound
  • CBC blood tests

The tests are performed in order to detect neural tube defects, Down Syndrome, spina bifida, anencephaly, and more. Some of these tests are standard (and fun!) — like the anatomy ultrasound where you get to check out all of baby’s development and discover your baby’s sex! Others, such as amniocentesis, have a very high level of risk and should be discussed with your doctor. For a full list of these tests, how they’ll be done, why they’re performed, and if they’re mandatory, read my article about second trimester tests.

What’s going on with baby during the second trimester?

By the end of the second trimester, your baby can hear, their digestive system is working, and they could be close to two pounds. Baby’s nervous system is continuing to mature and they’re still gaining fat. Get ready — baby will be kicking and jabbing soon!

Pregnancy week by week – 27 weeks pregnant – Mama Natural

When Does the Third Trimester Begin?

There’s some confusion as to when the third trimester begins. Some experts count by weeks, which would start the third trimester at week 27. Others count by months, which would start the third trimester at 28 weeks. Mama Natural begins the third trimester at week 28, which means the third trimester is thirteen weeks long.

What to expect during the third trimester

During the third trimester your healthcare provider may perform the following tests:

Sometimes the glucose test and other tests for gestational diabetes are performed earlier, or in week 27, if you are at high risk for developing it. More information on these tests can be found here.

What Week is Normal for Delivery?

“About 60 out of 100 women give birth on or before their given due date. In another 35 out of 100 women, contractions start on their own within two weeks of the due date. But it takes longer in about 5 out of 100 women.” (source)

It’s impossible to answer that big question — how long is pregnancy — with exact certainty, but a baby who is between 37 and 42 weeks gestation is considered term. There are, however, some nuances you’ll want to know about:

  • A baby born between 37 weeks and 38 weeks 6 days is considered early term
  • A baby born between 39 weeks and 40 weeks 6 days is considered full term
  • A baby born during the 41st week of pregnancy is considered late term
  • And a baby born 42 weeks or later is considered post term

By 37 weeks, it is generally safe to deliver baby if you go into labor. By this time, baby is fully formed, and has begun to move down into the pelvis in preparation for birth. Many midwives need babies to be at least 36 weeks, if not 37 weeks, to do a home birth.

However, unless there is a significant medical reason to do so, newer recommendations say induction and C-sections should not happen before baby reaches full term. Research shows that babies born at 37 weeks have more of a risk of complications, such as difficulty breathing, than those born just two weeks later.

Surprising Factors That May Affect the Length of Your Pregnancy

How long is pregnancy? It’s hard to say for sure, because it differs slightly from mama to mama and even pregnancy to pregnancy.

A family history of late deliveries is the biggest predictor of whether your pregnancy will go long. Not just your mother, sisters, or grandmother’s, but also the women in your male partner’s family. (source)

Other commonalities between mothers who had longer pregnancies include:

  • First-time pregnancy
  • Older maternal age
  • Higher education level of the mother
  • Higher weight gain during pregnancy
  • Higher BMI before pregnancy
  • Longer time between ovulation and implantation
  • Having a boy (really!)
  • If your baby measures small at ultrasounds during weeks 10-24
  • Environmental stressors during the last few weeks of pregnancy

If your pregnancy goes past 42 weeks, your healthcare provider may decide to induce.

What’s the Big Deal About Delivering After 42 Weeks?

If you’re approaching 42 weeks and you’re still asking yourself that big question — how long is pregnancy? — there’s good news: The answer is not much longer. Once you reach 42 weeks, the risk of complications rises and your midwife or doctor may decide to induce. (source)

Possible complications include:

  • Slowed/stopped growth because baby runs out of room
  • C-section due to baby’s size
  • Dropping levels of amniotic fluid, so less protection for baby
  • Fetal distress in the form of a slowed heartbeat or breathing problems
  • Meconium aspiration
  • Stillbirth

How Many Weeks is the Average First-Time Pregnancy?

How long is pregnancy? Surprisingly, that answer depends on how many times you’ve delivered a baby.

One study showed that a first-born baby has a 15 to 16 percent chance of being born late, compared with a 9 or 10 percent chance for other babies. However, the study also found that firstborns were also more likely to be born early, at 37 weeks or earlier. (source)

What does that tell you? Overall, firstborns are less likely to be born on time. Hang in there, Mama! ?

What If I Go Past My Due Date?

If you’re a few days late, you’re probably wondering: How long is pregnancy really?? I know you can’t wait to meet baby, but try not to stress it. If you go a week or two past your due date, you may really start to get antsy, but remember this is still considered normal.

Listen to your intuition, practice meditation and birth affirmations to ease your stress, and call your midwife or doctor if you have any questions of concerns.

How About You?

How long was your pregnancy?

Genevieve Howland

About the Author

Genevieve Howland is a childbirth educator and breastfeeding advocate. She is the bestselling author of The Mama Natural Week-by-Week Guide to Pregnancy and Childbirth and creator of the Mama Natural Birth Course. A mother of three, graduate of the University of Colorado, and YouTuber with over 85,000,000 views, she helps mothers and moms-to-be lead healthier and more natural lives.

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