At 13 weeks, you’re crossing the threshold into the second trimester, and for many people this is when pregnancy starts to feel noticeably easier. Nausea and exhaustion often begin to lift, miscarriage risk drops sharply, and your baby is now roughly the size of a lemon. Here’s what’s happening with your body and your baby this week.
How Your Baby Is Developing
By the start of week 13, the average fetus measures about 68 mm (just under 3 inches) from crown to rump, growing to nearly 79 mm by the end of the week. That’s rapid growth, roughly a millimeter and a half every day. The head, which was disproportionately large earlier, is starting to look more balanced as the body catches up.
Several important developments are underway. Ridges are forming on the palms and soles of your baby’s feet, laying the groundwork for unique fingerprints and footprints. The bones are beginning to harden, particularly in the skull and long bones, which is why calcium intake becomes more important now. The intestines, which temporarily bulged into the umbilical cord during earlier weeks, have moved into the abdomen where they belong. Your baby can also swallow amniotic fluid and produce small amounts of urine, signs that the digestive and urinary systems are starting to practice their jobs.
What’s Changing in Your Body
Your uterus is now rising out of your pelvis. At about 13 to 14 weeks, the top of the uterus sits just above your pubic bone. You may not have an obvious bump yet, especially with a first pregnancy, but your lower abdomen likely feels firmer and your regular pants are probably getting tight. Some people pop seemingly overnight in the next few weeks as the uterus continues to climb upward.
Hormonal shifts can trigger skin changes around this time. You might notice the beginnings of a faint dark line running down the center of your belly, called the linea nigra. It’s caused by increased melanin production driven by the placenta’s hormones. For most people it doesn’t become clearly visible until around 20 weeks, but the process is already starting. The same melanin surge can darken your areolas and, in some cases, create patches of darker skin on your face.
Symptoms That Are Shifting
The hallmark of week 13 is relief. Most people find the second trimester significantly easier than the first. Nausea and fatigue, the two most disruptive first-trimester symptoms, typically begin fading now. That doesn’t mean they vanish overnight. Some people still deal with lingering morning sickness into week 14 or 15, and a smaller number experience it throughout pregnancy. But the general trend is a noticeable uptick in energy and appetite.
New symptoms may replace old ones. As your uterus grows and your blood volume increases, you might notice occasional dizziness when you stand up quickly. Heartburn and indigestion can ramp up because the hormone relaxin loosens the valve between your stomach and esophagus. Breast tenderness from the first trimester often eases, though your breasts will continue to grow. Some people also notice increased vaginal discharge, which is normal as long as it’s clear or white and doesn’t have a strong odor.
Miscarriage Risk Drops Significantly
One of the most reassuring milestones at 13 weeks is the statistical shift in pregnancy loss. About 80% of all miscarriages happen within the first 13 weeks. Once you enter the second trimester, the risk drops to between 1% and 5%. This is the reason many people choose this point to share pregnancy news more widely. If you’ve had a healthy ultrasound showing normal development and a strong heartbeat, the odds are very much in your favor from here.
Prenatal Screening: A Time-Sensitive Window
If you haven’t yet had a nuchal translucency (NT) scan, week 13 is your last chance. This ultrasound measures a small pocket of fluid at the back of the baby’s neck to screen for chromosomal conditions like Down syndrome. The scan can only be done between 11 and 13 weeks because the fluid gets reabsorbed after 14 weeks, making it impossible to measure accurately. The NT scan is typically combined with a blood test as part of first-trimester screening. If you’ve been debating whether to do it, talk with your provider now rather than waiting.
Some people at this stage are also offered or considering cell-free DNA screening (a blood draw that analyzes fragments of fetal DNA circulating in your blood). This can be done any time after 10 weeks, so there’s no rush, but many providers order it around this time if it hasn’t been done already.
Weight Gain and Nutrition
Total weight gain during the first trimester is typically modest, somewhere between 1 and 4.4 pounds. Starting now, the recommended pace picks up. For someone who started pregnancy at a normal weight, the target is about 1 pound per week through the second and third trimesters. If you started at a higher weight, the recommendation is closer to half a pound per week.
Your baby’s skeleton is hardening rapidly, which makes calcium especially important. The fetus needs between 50 and 330 mg of calcium daily for bone development, and that demand increases as pregnancy progresses. The World Health Organization recommends pregnant adults aim for 1,500 to 2,000 mg of calcium per day. Dairy products, fortified plant milks, leafy greens, and canned fish with bones (like sardines) are all good sources. If you’re not consistently hitting that range through food, a supplement can fill the gap.
With nausea easing, this is also a good time to refocus on overall diet quality. Iron-rich foods, omega-3 fatty acids from fish or algae sources, and plenty of fiber for the constipation that often worsens in the second trimester are all worth prioritizing.
Exercise and Movement
Exercise is safe and beneficial for most pregnancies, but week 13 is a reasonable time to start adjusting your routine. Your center of gravity is beginning to shift forward as your uterus grows, which puts extra stress on your pelvis and lower back and makes you slightly more prone to losing your balance. High-impact or jerky movements carry more injury risk than they did a few weeks ago.
One important change: start avoiding exercises that keep you flat on your back for extended periods. In the supine position, your growing uterus can press on a major vein that returns blood to your heart, potentially causing a drop in blood pressure and dizziness. This becomes more relevant as the uterus gets heavier, but building the habit now is smart. Standing completely still for long stretches can cause blood to pool in your legs with a similar effect, so keep moving during workouts rather than holding static positions.
Walking, swimming, prenatal yoga, and moderate strength training are all excellent choices. If you were active before pregnancy, you can generally continue what you were doing with modifications. If you’re starting from scratch, even 20 to 30 minutes of brisk walking most days makes a measurable difference in energy levels, sleep quality, and how your body handles the later stages of pregnancy.