The second trimester runs from week 14 through week 27 of pregnancy. More precisely, the American College of Obstetricians and Gynecologists defines it as 14 weeks and 0 days through 27 weeks and 6 days. This is the middle stretch of a roughly 40-week pregnancy, and it’s often called the most comfortable trimester because early pregnancy symptoms like nausea tend to fade while the physical demands of the third trimester haven’t yet kicked in.
Why Some Sources Say Week 13
If you’ve seen conflicting answers online, you’re not imagining it. Some pregnancy apps and websites place the start of the second trimester at week 13 instead of week 14. This happens because 40 weeks don’t divide evenly into three parts. One common approach simply splits the pregnancy into three blocks of roughly 13 weeks each, which puts the second trimester starting at week 13. ACOG’s clinical definition, which most OB-GYN offices follow, uses week 14 as the cutoff. The practical difference is small, but if your provider references a specific trimester for scheduling tests or tracking milestones, they’re almost certainly using the week 14 start date.
What’s Happening to the Baby
By the time the second trimester begins, all of the baby’s organs, limbs, bones, and muscles are already present. The work of these 14 weeks is growth and refinement rather than formation from scratch. At week 14, the skin starts to thicken and fine hair begins to grow. By week 16, the lips have formed and the ears are developed enough to pick up sound, including your voice. By week 18, the baby is covered in lanugo, a soft peach-fuzz hair that helps regulate temperature.
Around week 22, the baby can hear your heartbeat, your breathing, and even your stomach rumbling. Its grip is strong enough to grasp the umbilical cord. By the end of the trimester at week 27, the baby has gone from roughly the size of a lemon to the size of a head of cauliflower, gaining substantial weight and moving constantly.
When You’ll Feel the Baby Move
One of the most anticipated milestones of the second trimester is quickening, the first time you feel the baby move. If you’ve been pregnant before, you may notice it as early as 16 weeks. First-time mothers typically don’t feel movement until around 20 weeks. Early movements often feel like flutters, bubbles, or a light tapping rather than distinct kicks. The sensation becomes stronger and more recognizable as the weeks go on.
Changes in Your Body
The relief many people feel in the second trimester comes from a hormonal shift. Levels of hCG, the hormone responsible for much of the first-trimester nausea, drop significantly. Your body adjusts to the rising levels of estrogen and progesterone, which continue climbing but no longer cause the same queasiness.
Those hormones do bring their own effects. Increased blood flow to your mucous membranes can cause nasal congestion and nosebleeds. Your gums may become spongier and bleed more easily when you brush. Some people develop darker patches of skin on the face or a dark line running down the abdomen, both caused by pregnancy hormones stimulating pigment production.
Your uterus becomes noticeable through the abdominal wall around 12 weeks, and by 20 weeks it reaches the height of your belly button. This is when pregnancy becomes visible to others. That rapid uterine growth stretches the round ligaments, two cord-like bands that support the uterus. The stretching can cause sharp, jabbing pains in your lower belly or groin, especially when you stand up quickly, cough, or roll over in bed. Round ligament pain is one of the most common second-trimester complaints and is harmless, though it can be startling.
Weight Gain During These Weeks
Steady weight gain becomes more important starting at week 14. If you began pregnancy at a healthy weight, the general guideline is about 1 pound per week through the rest of pregnancy. If you started out overweight or obese, the recommendation drops to about half a pound per week during the second and third trimesters. These are averages, not targets to hit precisely each week. Some weeks you’ll gain more, some less. The overall trend matters more than any single weigh-in.
Key Tests and Screenings
The second trimester includes some of the most important prenatal appointments. The biggest one is the anatomy scan, an ultrasound typically done between weeks 18 and 22. During this scan, a sonographer measures and photographs the baby’s heart, brain, spine, kidneys, limbs, and facial features. They also check the placenta’s position, the amount of amniotic fluid, and blood flow through the umbilical cord. This is often the appointment where parents can learn the baby’s sex if they want to know.
Toward the end of the second trimester, between weeks 24 and 28, most pregnant people are screened for gestational diabetes with a glucose challenge test. You drink a sugary solution and have your blood drawn an hour later to check how your body processes the sugar. If results come back high, a longer follow-up test determines whether gestational diabetes is present. The test may be done earlier if you have risk factors like a family history of diabetes or elevated glucose in your urine at routine visits.
The Tdap vaccine, which protects the newborn against whooping cough, is recommended during weeks 27 through 36. Providers often bring it up near the tail end of the second trimester so it can be given during the earlier part of that window, giving your body more time to produce antibodies that pass to the baby before birth.
A Week-by-Week Quick Reference
- Weeks 14–16: Skin thickens, baby begins hearing, round ligament pain may start, previous mothers may feel quickening.
- Weeks 17–20: Baby covered in lanugo, uterus reaches belly button, first-time mothers begin feeling movement.
- Weeks 18–22: Anatomy scan window.
- Weeks 22–24: Baby responds to sound, grip strengthens.
- Weeks 24–28: Gestational diabetes screening, Tdap vaccine discussion begins, baby gains weight rapidly as the trimester closes at week 27.