Your Pregnancy Week by Week

Welcome to Verywell’s Pregnancy Week-by-Week Guide. Your body is designed to do amazing things, but it’s fairly safe to say that all that happens in the 40 weeks of pregnancy are among the most incredible. While it may sometimes seem like not much is going on (and quite the contrary at other times), each week brings changes big and small that help your baby develop and your body prepare for labor, delivery, and beyond.

Pregnancy is marked by three trimesters:

The overviews in this guide provide a glimpse into all you can anticipate with each passing week of these distinct and important phases of your pregnancy, including:

  • How your body is changing
  • How your baby is growing
  • What to anticipate at your healthcare practitioner’s office
  • Special concerns and considerations to be aware of
  • The best ways to take care of yourself and your baby

And each week comes with a handy checklist so you can be sure you’re focusing on the most important tasks at hand.

Whether this is all new to you or a refrain, you may find pregnancy to be amazing, confusing, overwhelming, and everything in between (sometimes at the same time). We walk you through all you’re about to encounter, step by step, empowering you with what-you-need-to-know, when-you-need-to-know-it information that can help you make sense of it all—and make the decisions that are best for you and your baby.

Partners can find a special section dedicated to them each week, too. The 40 weeks of pregnancy can leave you with questions just the same, and we’re here to help.

Start by reading on to get a sense of what each trimester entails, then dig into the week-by-week overviews for a closer look at what a difference seven days can make. May your nine months of pregnancy be the healthiest and happiest they can be. We’re honored to be along for the ride.

First Trimester (Weeks 1 to 13)

While this portion of your pregnancy spans three months, it’s considered the shortest trimester. The reason? Many women don’t realize that they’re pregnant for the first month. (Home pregnancy tests generally will not register a positive result until about week 4.) Moreover, week 1 and week 2 are actually the weeks you ovulate and have your menstrual period. So, while the duration of pregnancy consists of 40 weeks, the countdown starts roughly two weeks before you officially become pregnant. (Confusing, we know.)

Your telltale baby bump won’t arrive until your second trimester, but you may notice outward signs of pregnancy before then, like swollen breasts and skin changes. While you may experience some belly changes, this is usually due to pregnancy-related bloating and gas, not baby growth. Still, by the end of your first trimester, you’ll likely have gained between 1 and 4½ pounds.

While your first trimester doesn’t yield much in the way of outward physical changes, a lot is happening that cannot be seen.

Day one of your pregnancy, the sperm and egg have yet to meet. By week 6—halfway through your first trimester—your baby’s tiny face, skull, and brain start to form. His or her hands and feet make their bud-like debut on baby’s tadpole- esque body. By the close of the first trimester, your baby is more than 3 inches long and sports arms, legs, eyes, a beating heart, and more. In fact, all of baby’s organs, muscles, limbs, and even genitals are represented. (You won’t learn what your baby’s sex is, however, until week 20.) His or her circulatory and urinary systems are functioning; baby’s skeleton begins the slow process of calcifying; his or her bone marrow is producing white blood cells; and your baby’s vocal cords are progressing toward maturity.

As for you, the pregnancy hormone human chorionic gonadotropin (hCG) is coursing through your body, doubling every two to three days and peaking at week 10. It’s produced by cells in your growing placenta and spurs the release of the hormones estrogen and progesterone, too. All of this contributes to a myriad of possible (but not guaranteed) early pregnancy symptoms such as nausea, fatigue, and heartburn. These symptoms tend to wane come your second trimester, when hCG levels off.

You’ll begin your prenatal appointments this trimester, of course, so it’s important that you have a practitioner you are confident in and comfortable with. There’s no rule that states that the provider who has been giving you your annual check-ups and Pap smears needs to be the one you see throughout pregnancy.

If you haven’t already, take this time to start looking into the difference between OB/GYNs and midwives, and ask friends and family for recommendations. Once you settle on a practitioner, you can expect to see him or her every four weeks until the conclusion of your second trimester. (At that point, your visits increase in frequency.)

While you may be looking forward to seeing a sonogram image of your growing baby during your first trimester, you might not be able to. For a majority of pregnant women, a first-trimester ultrasound is not considered a must-do, so you may not see your baby-to-be’s picture until your second trimester. Rest assured, if everything is on track, your baby is developing at a rapid speed right now.

Second Trimester (Weeks 14 to 27)

For most moms-to-be, this in-the-middle trimester is considered the easiest. The reason: Your newly-formed placenta is generating more progesterone, a hormone needed to keep your uterine lining baby-friendly. And this progesterone-boost allows for a decrease in the production of symptom-causing hCG. As such, you may feel like your pre-pregnancy self again, enjoying an uptick of energy and appetite.

Regardless of your appetite, most women can expect to gain about one pound a week during the second trimester, putting total weight gain at about 12 to 14 pounds by the end of week 27.

Your chance of miscarriage drops to between 1 percent and 5 percent in the second trimester, according to the March of Dimes. Armed with that knowledge, many parents-to-be now decide to share their big news with a wider circle. 

About halfway through your second trimester, you’ll experience many milestone moments. For instance, the baby bump you’ve been anticipating will probably become visible to others around week 20. (Maternity clothes are now in full rotation.) That’s also about the same time you’ll likely start to feel your baby’s first movements. (You may show—and feel movement—a couple of weeks earlier if this is not your first child.) While your baby’s sex will already be determined by the start of your trimester, baby-to-be’s genitals aren’t detectable on an ultrasound until week 18 to week 20.

It’s true that your second trimester likely has you feeling better than the first, but it’s not exactly symptom-free. For instance, as your trimester nears its end, you may start to feel practice uterine contractions, called Braxton Hicks. Hormones continue to flow, and your baby steadily grows, taking up more and more room (and forcing your body to accommodate).

While every woman is different, here are some not-so-welcome pregnancy side effects you may be faced with during your second trimester:

  • Frequent urination
  • Back pain; sciatic nerve pain
  • Low blood pressure
  • Leg cramps
  • Round ligament pain (This involves ligaments that stretch from the top of your uterus to either side of your pelvis.)
  • Racing heart

Though not painful, you may also notice varicose veins and skin changes, such as mole growth and stretch marks.

Regardless of how you are feeling, there’s a lot happening with your baby during this time. He or she kicks off your second trimester at a mere one ounce and closes it out at 2¼ pounds. Your baby will also have grown more than 10 inches, measuring 13¾ inches long by trimester’s end.

During this period of tremendous growth, your baby-to-be’s liver, spleen, and thyroid all begin to take on their respective responsibilities. Baby’s brain and nerve endings are mature enough that he or she can now feel touch. His or her soft and flexible skeleton begins to ossify, or harden. And by roughly week 22, his or her tiny heartbeat can actually be heard if your partner puts his or her ear to your abdomen—perhaps some hiccups, too—since your baby is busily swallowing amniotic fluid now. At the same time, baby’s auditory system is developed enough that he or she may be able to hear you, too.

By the end of your second trimester, your baby looks a lot like the person you will meet at week 40, albeit much smaller and more wrinkly: Baby’s eyes and ears have moved to their intended location and his or her arms and legs are now proportionate to rest of the body. And, perhaps most exciting, you’ll be able to see your baby-to-be during this trimester, thanks to an ultrasound taken around week 20.

Though week 40 seems far away, now is the time to book a childbirth class and start to think about childcare and your maternity leave, if you work outside the home. You’re also closing in on your final opportunity to travel, both comfortably and with your practitioner’s blessing.

Third Trimester (Weeks 28 to 40)

While you may be pregnant for the entirety of the third trimester, the majority of women go into labor between week 37 and week 39, with the rest going earlier or as late as 42 weeks. Meanwhile, the average twin pregnancy delivers at about 35 weeks. No matter which category you will fall into, the literal heft of your baby and the emotional load of your impending birth and changing role make this final leg of pregnancy the most physically and emotionally challenging.

It’s also a very exciting trimester. When your partner places his or her hand on your belly, he or she can now feel your baby move from the outside. And there’s a lot to feel since baby’s movements are more frequent now. Soon, you’ll actually be able to see baby’s kicks and flutters through your belly, too. For many moms-to-be, this is also when the shower is thrown, the nursery is put in order, and nesting kicks in.

At the start of your third trimester, you’ve likely gained between 17 and 24 pounds. This steady uptick of the scale continues for about two more months. Then, around week 37, your total weight gain will likely hold steady between 25 and 35 pounds.

The increase of total weight, plus the fact that your belly is pulling your spine forward, can amplify back pain. Meanwhile, your crowded and ballooning uterus is putting pressure inside your abdomen, possibly spurring hemorrhoids, and likely pressing on your diaphragm, hindering breathing and increasing heartburn. At the same time, your lungs and intestines have also shifted positions in order to accommodate your growing baby.

All of this can cause aches, ouches, and disrupted sleep. However, midway through your final trimester, you may experience some relief by way of lightening, a term used for when your baby drops lower into the birth canal. Unfortunately, baby’s downward shift then increases pressure on your bladder.

As you inch closer and closer to delivery day, you’ll notice subtle changes in your body. For instance, Braxton Hicks contractions may occur more frequently now. And around week 31, your breasts may begin to leak a creamy yellow or a thin, watery substance called colostrum. In addition, your body is now churning out the hormone relaxin, which loosens the ligaments and bones in your pelvis, allowing for baby to exit smoothly—and also spurring late-in-pregnancy clumsiness. Your estrogen levels are increasing in order to soften (efface) and open (dilate) your cervix. As a result, your mucus plug, which has been shielding your cervix from bacteria, begins to thin.

And, of course, the grand finale of the third trimester is labor and delivery. You’ll know when labor kicks in when you begin to experience real contractions.

While you’re going through all of these major changes leading up to delivery day, so is your baby. This is a time of accelerated growth and finishing-touches development. Your baby will have gained roughly 5 pounds in the 12 weeks that make up this final trimester, starting at just over 2 pounds and being born at roughly 7 pounds.

Up until the third trimester, the surface of your baby-to-be’s brain was nearly smooth. Now, thanks to developing brain tissue, it’s filled with grooves and folds. And it continues maturing throughout this trimester, growing by a third between week 35 and week 39. Baby’s lung and liver are steadily developing during these later weeks, too.  Since the brain, liver, and lungs need one more week to mature, your baby is considered “early term” if born between week 37 and week 38. Finally, baby’s bones are fully formed, but the plates in baby’s skull remain malleable in order for your baby to pass through the birth canal with ease. By week 39, your baby will not become any more physically ready for birth. Instead, he or she uses this time to properly position him or herself for labor.

All the while, your healthcare provider will be keeping close tabs on both you and your baby. Come the third trimester, your prenatal appointments shift from once every four weeks to twice a month. Then, around week 36, you’ll begin to see your physician or midwife every week.

Labor and Delivery

If everything goes according to plan, you will deliver at around 40 weeks, though many women do so before or after. Your delivery may follow your birth plan to the letter or look entirely different than you have imagined it, perhaps, ending in a C-section when you intended to have a vaginal birth.

Regardless, your body (if not your mind) has been preparing for this moment throughout the course of your pregnancy. Take comfort that you have selected a healthcare practitioner that you can count on, lean on your support team, and communicate your wishes for pain management and more. Reading the overviews of the final weeks of pregnancy in this guide can help you better understand different labor and delivery scenarios and what you can expect, both during and after.

This day may seem forever away, but it will be here before you know it. And what may have sometimes seemed like the long road you took to get there will be all worth it.

Up First: Week One

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