You Made It Through
Here you are. Week 13. The second trimester begins.
That phrase, "the second trimester," gets used so often in pregnancy conversations that it can start to feel like a formality. It is not. The transition from the first to the second trimester is one of the most clinically significant milestones in early pregnancy. The risk of pregnancy loss, which was most concentrated in the first eight weeks, drops substantially once you cross into week 13 [3]. For women who have had a confirmed healthy fetus on ultrasound, that risk is now lower than it has been at any point since the positive test.
You earned this week. The nausea, the secrecy, the exhaustion, the fear. The first trimester is behind you.
Your Baby This Week
Your fetus measures approximately 2.9 inches (7.4 cm) from crown to rump and weighs about 0.81 ounces (23 grams), roughly the size of a peapod [2]. The body is finally starting to catch up with the head, which has been disproportionately large throughout the first trimester as the brain developed rapidly.
Vocal cords are forming in the larynx this week [1]. Your baby will not make sound in the womb, but the structures for eventual sound production are taking shape. At the same time, unique fingerprints are forming on the tiny fingertips, created by the specific pattern of skin ridge growth that is entirely individual [2]. No other person who has ever lived, or who will ever live, will have the same fingerprints.
The placenta is fully functional this week and has taken over a critical role: producing progesterone, the hormone that has been maintaining the pregnancy [1]. Up until now, the corpus luteum (the structure left in the ovary after ovulation) was the primary source of progesterone. The placenta's takeover of this function is one reason many women feel significantly better around this time. The hormonal production is shifting to a more stable source, and hCG levels, which drove much of the nausea, are starting to decline.
Bone ossification continues throughout the skeleton. The intestines, which spent the past several weeks partially developing in the umbilical cord due to space constraints, are completing their migration into the abdominal cavity as it enlarges [2].
What the Second Trimester Actually Means
The second trimester runs from week 14 through week 27. It has a well-earned reputation as the "honeymoon period" of pregnancy, and while that experience varies, the physiological changes are real.
The pregnancy loss risk data is worth understanding clearly. Overall pregnancy loss risk in the first trimester (before week 13) is approximately 10 to 15% for confirmed pregnancies [3]. After a heartbeat has been seen on ultrasound and you reach week 13, that risk drops to under 1% for otherwise healthy pregnancies. This is the data behind "waiting until the second trimester to announce," though there is no rule requiring you to wait or to announce on any particular schedule.
Several welcome changes are typical in the early second trimester:
Nausea fades for most women. The hCG decline that begins around now, combined with the corpus luteum handing off progesterone production to the more stable placenta, is why nausea typically improves between weeks 12 and 16 for most women [1]. Not for everyone, and "fading" does not always mean "gone," but the trend is real.
Energy returns. The crushing first-trimester fatigue driven by high progesterone and the intense early developmental work often lifts in the second trimester. Many women describe feeling closer to normal than they have since before the positive test.
The bump becomes visible. Most women begin to show more noticeably in the second trimester as the uterus grows above the pelvic brim.
Your Body at Week 13
- Energy returning. If you notice you are sleeping less desperately and functioning better during the day, this is the expected second-trimester shift.
- Nausea improving. Still present for some women, and a few will continue to experience nausea into the second trimester [3]. This is not abnormal and does not indicate a problem with the pregnancy.
- Visible bump forming. The uterus is rising out of the pelvic cavity. How visible this is depends on your body type, your abdominal muscles, and whether this is your first pregnancy.
- Round ligament pain. As the uterus expands, the round ligaments that support it can cause brief, sharp pains on one or both sides of the lower abdomen, especially with sudden movements or position changes.
- Skin changes. Melasma (darkening patches on the forehead, cheeks, and upper lip), darkening of the linea alba (a vertical line down the center of the abdomen), and continued areola darkening are all hormonally driven and typically fade after delivery.
Starting Exercise in the Second Trimester
If the first trimester was too rough for much physical activity, week 13 is a reasonable time to ease back in. ACOG recommends 150 minutes of moderate-intensity aerobic activity per week for women with uncomplicated pregnancies [4]. Walking, swimming, prenatal yoga, stationary cycling, and low-impact aerobics are all appropriate starting points.
If you have any pregnancy complications, ask your provider before beginning or resuming an exercise program. The recommendation for 150 minutes is the general guideline; your individual situation may call for modifications.
Eating continues to matter in the second trimester, perhaps more than in the first when nausea may have limited your intake. The second trimester requires an additional approximately 340 calories per day above your pre-pregnancy baseline [5]. Focus on protein, calcium, iron, and omega-3 fatty acids. Your prenatal vitamin handles many micronutrients, but whole food sources are the foundation.
"I'm starting to show and now everyone has an opinion about my body." The transition from invisible pregnancy to visible pregnancy changes how the world interacts with you. Colleagues comment on your size. Strangers offer unsolicited predictions. Your body becomes public conversation in a way it never was before. The discomfort you feel is not oversensitivity. It is a normal response to a sudden loss of physical privacy. You are allowed to set boundaries. "I'd rather not discuss my body" is a complete sentence.
What MomDoc Wants You to Know
The second trimester brings more appointments, more milestones, and, for many women, more enjoyment of the pregnancy itself. Your next routine visit is typically around week 16, where your provider will measure your uterus, check the heartbeat, and review any screening results you are waiting on.
If you are still feeling terrible and waiting for the nausea to end, it is okay to call and ask for help. There are effective treatments for persistent nausea in the second trimester, and you do not need to simply wait it out.
Workplace conversations, social conversations, the question of when and how to tell people: there is no right answer. You get to decide your timeline, your framing, and how much you share with whom. What you have accomplished in the first 13 weeks, growing an entire set of organs, a placenta, and a person with fingerprints, is extraordinary regardless of who knows yet.
The second trimester is yours. Welcome to it.