The second trimester of pregnancy is three months long, spanning months four, five, and six. In terms of weeks, it covers weeks 13 through 27 (or sometimes defined as 14 through 27, depending on the source). This middle stretch of pregnancy is often called the “honeymoon trimester” because many of the rough early symptoms ease up and energy returns.
How Weeks Map to Months
Pregnancy math can feel confusing because months and weeks don’t divide evenly. A pregnancy month isn’t exactly four weeks long, since most calendar months have 30 or 31 days. Here’s a rough breakdown of how the second trimester maps out:
- Month 4: Weeks 13 through 16
- Month 5: Weeks 17 through 20
- Month 6: Weeks 21 through 24
Weeks 25 through 27 bridge the transition into the third trimester. Some providers count week 27 as the final week of the second trimester, while others place it at the start of the third. The slight variation depends on which clinical guideline your provider follows, but the difference is only a week or so and doesn’t change your care.
What Happens to Your Baby
Your baby goes through dramatic changes during these three months. At the start of the second trimester, the fetus is roughly three inches long. By the end, it’s around 14 inches and weighs close to two pounds.
Around 18 weeks, your baby’s ears begin to stand out from the head and hearing starts to develop. By about 21 weeks, a sucking reflex kicks in, which is why ultrasounds sometimes catch babies sucking their thumbs. Around 23 weeks, ridges form on the palms and soles that will become unique fingerprints and footprints.
One of the most exciting milestones is quickening, the first time you feel your baby move. This typically happens between 16 and 20 weeks. If you’ve been pregnant before, you may notice it closer to 16 weeks. First-time pregnancies often don’t produce recognizable movement until around week 20. Early movements feel like flutters or bubbles, and they gradually become stronger kicks and rolls as the weeks progress.
How Your Body Changes
The fatigue and nausea that dominate the first trimester usually fade in the second trimester, replaced by a noticeable boost in energy and a general feeling of well-being. That doesn’t mean you’re symptom-free, though. As your uterus expands, you may feel aches in your back, abdomen, groin, and thighs. Round ligament pain, a sharp or stabbing sensation on the sides of your lower belly, is one of the most common complaints and happens because the ligaments supporting your uterus are stretching to accommodate growth.
Skin changes also become more visible. Stretch marks, typically red, pink, or brown streaks, often appear on the abdomen, breasts, thighs, and buttocks during the second half of pregnancy. Many women notice a dark vertical line running from the belly button to the pubic area, called the linea nigra. Darker patches of skin on the cheeks, forehead, nose, or upper lip are also common, especially in women with darker skin tones. Nipples often darken as well. Most of these changes fade after delivery, though some may linger.
Weight Gain and Nutrition
Steady weight gain becomes more important starting around week 14. If you began pregnancy at a healthy weight, the general guideline is to gain about one pound per week through the second and third trimesters. If you started out overweight, the recommendation drops to about half a pound per week during the same period.
Calorie needs increase modestly. Most normal-weight pregnant women need about 2,200 calories per day during the second trimester, roughly 300 extra calories compared to pre-pregnancy intake. That’s about the equivalent of an extra snack, not a second dinner. Focusing on nutrient-dense foods like lean protein, whole grains, fruits, and vegetables helps support the rapid fetal growth happening during these months.
Key Prenatal Screenings
Several important tests happen during the second trimester. Between weeks 15 and 20, a blood test called a quad screen measures four proteins in your blood to assess the risk of certain birth defects. The results don’t diagnose anything on their own but help your provider decide whether further testing is warranted.
The anatomy ultrasound, usually done around 18 to 20 weeks, is a detailed scan where a technician checks all of the baby’s major structures: the brain, heart, spine, kidneys, and limbs. This is also often the appointment where you can find out the baby’s sex if you want to know. A glucose challenge test is typically scheduled toward the end of the second trimester, around weeks 24 to 28, to screen for gestational diabetes.