The second trimester runs from week 13 through week 28 of pregnancy. If you’re trying to figure out whether you’ve crossed that line, the simplest way to think about it: once you finish week 12, you’re in your second trimester, and it lasts until the end of week 27 (with week 28 beginning the third trimester). This 16-week stretch is often called the “honeymoon phase” of pregnancy because many of the rough early symptoms ease up and energy levels improve.
How the Weeks Break Down
Pregnancy is divided into three trimesters of roughly equal length. The first trimester covers weeks 1 through 12, the second covers weeks 13 through 27, and the third runs from week 28 until delivery. Some sources define the second trimester as starting at week 14, which reflects slight differences in how organizations round the numbers, but week 13 is the most widely used starting point.
If you’re counting by months, the second trimester spans roughly months four through six. But “months” in pregnancy are unreliable because calendar months and four-week blocks don’t line up neatly. Weeks are more precise, and they’re what your provider uses to track your care.
Why You Start Feeling Better
The nausea, fatigue, and breast tenderness that define early pregnancy are largely driven by rapidly rising hormone levels during the first trimester. By around week 7, the placenta takes over progesterone production from the ovaries. By the time you enter the second trimester, your body has adjusted to these hormonal shifts, which is why many people notice a clear uptick in energy and appetite somewhere around weeks 13 to 16.
That said, the second trimester brings its own set of changes. As your uterus grows, you may feel sharp or pulling sensations in your lower abdomen from round ligament pain. Backaches become more common as your center of gravity shifts. Some swelling in your feet and ankles can start appearing, especially toward the later weeks of this trimester.
How Your Baby Grows During These Weeks
At week 14, the fetus is about 3.5 inches long (measured from head to tailbone) and weighs roughly 1.5 ounces. By week 26, that same measurement reaches about 9 inches, and weight climbs to nearly 2 pounds. That’s an enormous amount of growth in a short window, and it corresponds to some major developmental milestones.
In the early second trimester (weeks 13 to 16), fingernails and toenails form, the neck becomes more defined, and the genitals develop enough that they may be visible on ultrasound. The liver and pancreas are maturing, and the kidneys begin producing urine.
By weeks 17 to 20, the part of the brain controlling motor movement is fully formed. Hearing starts to develop, meaning your baby begins responding to sound. The skin is still thin and translucent but starts to thicken. Lung tissue that will eventually handle oxygen exchange begins forming, though the lungs won’t be functional for months.
Toward the end of the second trimester (weeks 24 to 27), the fetus reaches what doctors call the periviable period. Survival outside the womb becomes possible but still carries serious risks. At 23 weeks, survival rates range from 23% to 27%. At 25 weeks, that improves to 67% to 76%. These numbers underscore how critical each additional week of development is during this stage.
Feeling Your Baby Move
One of the most anticipated moments of the second trimester is quickening, the first time you feel your baby move. This typically happens between weeks 16 and 20, though the timing depends on whether you’ve been pregnant before. If this is a subsequent pregnancy, you may notice fluttering as early as 16 weeks because you recognize the sensation. First-time parents more commonly feel it closer to week 20.
Early movements feel like bubbles, light tapping, or a fluttering sensation that’s easy to mistake for gas. Over the following weeks, those movements become stronger and more distinct, eventually turning into kicks and rolls you can see from the outside.
Key Screenings in the Second Trimester
Two important tests are scheduled during these weeks. The anatomy scan, a detailed ultrasound performed between weeks 18 and 22, is the most comprehensive imaging your baby will receive before birth. A sonographer measures the heart, brain, spine, kidneys, limbs, and facial structures. They also check the placenta’s position, the umbilical cord’s blood flow, amniotic fluid levels, and your cervix. This is often when you can learn the baby’s sex if you want to know.
The glucose screening test comes later, between weeks 24 and 28. You’ll drink a sugary solution and have your blood drawn an hour later to check how your body processes sugar. This screens for gestational diabetes, which affects how your body regulates blood sugar during pregnancy and can influence your birth plan if detected.