Week 13
Your baby is the size of a peach
What's happening this week
Welcome to the second trimester — you've officially made it through the most uncertain phase of pregnancy. Your baby is now about the size of a peach, measuring roughly 2.9 inches (74mm) from crown to rump and weighing about 0.8 ounces.
This week brings a subtle but extraordinary development: your baby's vocal cords are forming. They won't produce sound until birth (the larynx needs air to vibrate), but the structures are being built now. Meanwhile, fingerprints — completely unique to your baby and different from every other person who has ever lived — are beginning to form on those tiny fingertips.
The head, which until now has been disproportionately large, is starting to become more proportional to the body. The skeleton is continuing to harden from cartilage into bone, particularly in the skull and the long bones of the arms and legs. If you had an ultrasound right now, you'd be able to see the skeletal structure clearly.
Your baby's intestines, which had temporarily extended into the umbilical cord during the first trimester, have now fully migrated back into the abdominal cavity where they belong. The kidneys are producing urine, and the liver is secreting bile — both organs actively practicing their future jobs.
One delightful detail: your baby can now turn their head. The neck muscles are strengthening, allowing more independent head movement. And though the eyes are still fused shut, they're now positioned at the front of the face rather than on the sides — giving your baby a distinctly human appearance.
Your body this week
If the first trimester was a marathon of nausea and exhaustion, the second trimester is where many people get their life back. You may notice that morning sickness is fading or gone entirely, food sounds appealing again, and the crushing fatigue has lifted. Not everyone experiences this shift at exactly week 13 — some people need another week or two — but the trend is heading in the right direction.
Your appetite is likely increasing, and that's a good thing. Your body is growing a human and needs the fuel. Most healthcare providers recommend an additional 340 calories per day during the second trimester — roughly the equivalent of a banana with peanut butter and a glass of milk. Focus on nutrient-dense foods rather than eating for two in volume.
Physically, your bump may be becoming more noticeable. The uterus is rising above the pubic bone, and your provider can now feel it during abdominal exams. You might notice a dark line appearing down the center of your abdomen — this is called the linea nigra, and it's caused by increased melanin production. It's completely normal and usually fades after birth.
Round ligament pain may continue — those sharp twinges when you stand up or turn quickly. Gentle stretching, moving slowly when changing positions, and a warm (not hot) bath can help.
This is a great time to start incorporating gentle exercise into your routine if you haven't already. Walking, swimming, and prenatal yoga are all excellent choices that most providers encourage throughout pregnancy.
For dads
The second trimester is here, and you might notice a real shift in your partner's mood and energy. The woman who could barely keep her eyes open after dinner last month may suddenly want to go for a walk, cook a real meal, or actually stay awake for a movie. This is the golden trimester — enjoy it. Use this energy window to tackle practical things together: start discussing nursery plans, research car seats, and think about whether you want to find out the baby's sex at the anatomy scan around week 20.
If you haven't shared the pregnancy news yet, this is the week many couples do it. Talk with your partner about who to tell, when, and how. Some couples tell family in person and do a social media announcement later. Others keep it private longer. There's no right way — but making this decision together matters. And if you're the kind of person who's been bursting to tell everyone for weeks, be patient if your partner wants to wait a bit longer. This is a shared decision, and her comfort level should carry significant weight.
Common concerns
Is it normal to feel so much better suddenly?+
Yes — the dramatic improvement many people feel at the start of the second trimester is one of pregnancy's most welcome shifts. hCG levels have plateaued and the placenta has taken over hormone production, which stabilizes many of the symptoms that made the first trimester difficult. Not everyone feels better at exactly week 13, but the general trend is toward more energy, less nausea, and improved mood over the coming weeks.
How much weight should I be gaining?+
Weight gain varies significantly from person to person. General guidelines suggest gaining 1-5 pounds total during the first trimester, then about 1 pound per week during the second and third trimesters. For someone who started pregnancy at a normal BMI, the total recommended gain is 25-35 pounds. But these are guidelines, not rules — your provider will track your weight and let you know if there are any concerns specific to your pregnancy.
Is it safe to sleep on my back during the second trimester?+
During early pregnancy, sleeping on your back is generally fine. As the uterus gets larger (usually after about week 20), sleeping on your back can compress major blood vessels and reduce blood flow to you and your baby. Most providers recommend sleeping on your side — particularly the left side — from the second trimester onward. A pregnancy pillow can make side sleeping more comfortable if you're naturally a back sleeper.
When should I tell my employer I'm pregnant?+
There's no legal requirement to disclose your pregnancy by a specific date, though many people tell their employer sometime during the second trimester. Consider your workplace culture, your physical demands, and any accommodations you might need. You'll want to discuss maternity leave plans before the third trimester. If you have safety concerns about your work environment (exposure to chemicals, heavy lifting, etc.), it's worth telling your employer sooner so accommodations can be arranged.
Product picks for week 13
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Pregnancy pillow (full body)
Side sleeping gets more important from here on — a full-body pregnancy pillow supports your belly, back, and hips all night.
Maternity wardrobe basics
Your regular clothes are getting tight — a few key maternity pieces (jeans, leggings, tops) will carry you through the next six months.
Prenatal yoga online class
Energy is returning and gentle exercise feels good again — prenatal yoga builds strength and flexibility you'll need for labor.
A quick note: This content is for informational purposes only and is not a substitute for professional medical advice. Always talk to your healthcare provider about any questions or concerns. Learn how we create our content.
Content based on guidance from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), Mayo Clinic, and peer-reviewed medical literature. Learn more about how we create our content.