Your baby this week
The lungs have come a long way but still need weeks to mature. Fat is building up under the skin, and the organs keep maturing.
Week 27 is the last week of the second trimester. Your baby's brain is growing fast, with more and more nerve connections forming. Sleep cycles are more regular, and your baby is often busiest just when you want to rest. For you, breathlessness and tiredness may return as your uterus takes up more room. If your blood type is Rh-negative, you'll typically be offered an anti-D (Rh immune globulin) shot around 28 weeks so your body doesn't make antibodies against your baby's blood. The Tdap vaccine against whooping cough is recommended between 27 and 36 weeks, ideally early in that window, so your baby is protected in the first months.
By the numbers
Week 27 covers days 189 to 195 counted from the first day of your last period, which is 68% of a 40-week pregnancy. About 91 days remain until a 40-week due date. Since last week, an average baby gains about 4.9 oz (138 g). By date of conception, your baby is about 25 weeks old.
Pregnancy is dated from the first day of your last period, so conception happens around week 2. Your due date is 280 days (40 weeks) from that day, and an early ultrasound may adjust it.
Your body
This is the last week of the second trimester. Mild breathlessness is common as your uterus pushes up, but sudden shortness of breath, or breathlessness with chest pain, needs emergency care (call 911).
Tests and to-dos this week
Tdap, the whooping cough vaccine, is recommended in every pregnancy between 27 and 36 weeks, ideally early in that window. It helps pass protective antibodies to your baby.
Glucose screening for gestational diabetes · weeks 24–28 · test
Done earlier if you have risk factors.
Tdap (whooping cough) vaccine · weeks 27–36 · vaccine
Recommended during each pregnancy, preferably early in this window.
Coming up: Rh immune globulin (if you're Rh negative) (from week 28). Full prenatal visit schedule
Tips for the second trimester
- Most healthy pregnant people are advised to get about 150 minutes of moderate activity a week, such as walking or swimming.
- Your recommended weight gain depends on your pre-pregnancy BMI, and gain usually speeds up in the second trimester.
- Once you feel your baby regularly, learn their usual pattern; a change in pattern matters more than any count.
- The flu shot is recommended at any point in pregnancy during flu season.
Call your provider or labor and delivery right away if you have:
- vaginal bleeding or leaking fluid
- regular contractions or pelvic pressure before 37 weeks
- a severe headache, vision changes, or sudden swelling of the face or hands
- a fever of 100.4 °F (38 °C) or higher, or painful urination
- after 24 weeks, your baby moving less or differently
In an emergency, call 911.
Last week and next week
Last week (26): Your baby's eyes open for the first time this week.
Frequently asked questions
How big is the baby at 27 weeks?
About the size of an eggplant: about 14.6 in (37 cm) · 2.3 lb (1,040 g), measured head to heel. These are rounded averages, and every baby grows at their own pace.
How many months is 27 weeks pregnant?
27 weeks is in month 6 and the second trimester. About 13 weeks (91 days) remain until a 40-week due date. Months are approximate; providers count weeks and days.
When should I get the Tdap vaccine?
The CDC recommends Tdap between 27 and 36 weeks in every pregnancy, ideally early in that window, so antibodies pass to your baby before birth.
What's the next test or appointment after week 27?
Next up: Rh immune globulin (if you're Rh negative), from week 28. Your provider may schedule things differently depending on your health and local practice.
Sources
- WHO Fetal Growth Charts (Kiserud et al., PLoS Med 2017)
- INTERGROWTH-21st crown-rump length standard (Papageorghiou et al., 2014)
- Hadlock et al.: In utero fetal weight standard (Radiology 1991)
- NHS: Week-by-week guide to pregnancy
- NHS: Pregnancy symptoms you need to get help for
- ACOG: How Your Fetus Grows During Pregnancy
- ACOG: Routine Tests During Pregnancy
- ACOG: Prenatal Genetic Screening Tests
- CDC: Vaccine Recommendations Before, During, and After Pregnancy
- Office on Women's Health: Prenatal care and tests
- Hungarian Decree 26/2014 (IV. 8.) EMMI on prenatal care
- NNGYK (Hungary): 2026 vaccination methodology letter
- ACOG – Group B Strep and Pregnancy (Committee Opinion 797)
- ACOG – The Rh Factor
Last reviewed: November 14, 2026 · Kitpebble editorial team
This page is for general information. It isn't medical advice or a diagnosis and doesn't replace your OB-GYN or midwife. Sizes are rounded averages. Our editorial policy