The second trimester is the middle of pregnancy, from about week 13 or 14 through week 27 or 28 depending on the source, when nausea often eases, your bump shows and you usually first feel your baby move.
Many people call this the easiest stretch of pregnancy, and the Office on Women’s Health agrees that most women find it easier than the first. It is also busy: big screening tests, a growing bump, first kicks and a lot of planning.
This guide covers the weeks and months, development and size, symptoms, tests, weight gain, exercise, travel, sex and sleep, with a link to every week. Every clinical detail was read in October 2026 on the primary sources named in the text.
Key Takeaways
ACOG, as reported by UPMC, defines the second trimester as 14 weeks 0 days through 27 weeks 6 days. The Office on Women’s Health uses weeks 13 to 28.
It covers about months 4, 5 and 6. At 13 weeks you have completed about 3 months.
UPMC says first movements are usually felt around 16 to 20 weeks.
Key tests: the quad screen (weeks 15 to 22), the anatomy ultrasound (around week 20) and glucose screening (weeks 24 to 28).
The CDC suggests about 340 extra calories a day. Call right away for bleeding, a severe headache, severe belly pain or strong cramps.
Table of Contents
When Does the Second Trimester Start and End?
Quick Answer
The second trimester is the middle of pregnancy, roughly weeks 13 or 14 through weeks 27 or 28, or about months 4, 5 and 6. By the American College of Obstetricians and Gynecologists (ACOG) definition, as reported by UPMC, it runs from 14 weeks 0 days through 27 weeks 6 days, about 14 weeks or 3.5 months. The Office on Women’s Health counts weeks 13 to 28, so both answers you see online are in use.
Source
Second trimester
Third trimester begins
ACOG, as reported by UPMC
14 weeks 0 days through 27 weeks 6 days
28 weeks 0 days
Mayo Clinic
Its second trimester guide runs from week 13 and says the trimester ends at week 27
After week 27
MedlinePlus (NIH)
Weeks 14 to 28
After week 28
Office on Women’s Health (HHS)
Week 13 to week 28
Week 29
When does the second trimester start and end? Definitions differ by source, so all four are printed.
Is 13 weeks the second trimester? For the Office on Women’s Health and Mayo Clinic, yes. By the ACOG definition it is the last week of the first trimester. Your care does not change on the day you cross the line, and our first trimester and third trimester guides use the same definitions.
How the weeks are counted. The Office on Women’s Health says pregnancy lasts about 40 weeks, counted from the first day of your last normal period, not from conception. That is why Mayo Clinic labels week 14 as 12 weeks after conception. If an early ultrasound moved your due date, use the adjusted dates.
Weeks to Months: How Many Months Is It?
Months are a counting convention, not a medical unit, which is why your provider talks in weeks. Counting about 4 weeks and a few days per month:
Month of pregnancy
About which weeks
Month 4
Weeks 14 to 17
Month 5
Weeks 18 to 22
Month 6
Weeks 23 to 27
The second trimester in months. Other guides draw the month lines a week earlier or later.
13 weeks pregnant in months. Thirteen weeks is 91 days, so you have completed about three months and are starting the fourth. Charts that use exact four-week months move every boundary earlier, so go by the weeks.
Baby Development and Size, Week by Week
UPMC sums up the trimester: the organs formed in the first trimester keep maturing, the kidneys start working, bone tissue and ears form, and the baby starts building fat stores. Your baby may suck a thumb and may begin to hear.
Weeks
What the sources say
13 to 15
Bones begin to harden around week 13 and should be visible on ultrasound by week 15 (Mayo Clinic).
16 to 18
Muscle and bone are forming and the baby makes sucking motions at 16 weeks (Office on Women’s Health). By week 18 the baby may begin to respond to sounds (Mayo Clinic).
19 to 21
A greasy, cheese-like coating forms over the skin around week 19, and fine downy hair covers the body around week 21 (Mayo Clinic). At 20 weeks the baby can hear and swallow (Office on Women’s Health).
22 to 24
Eyebrows and scalp hair show around week 22, and the lungs start making surfactant around week 23 (Mayo Clinic). At 24 weeks the lungs are formed but do not work yet (Office on Women’s Health).
25 to 27
The baby may move in response to your voice around week 25. By week 26 eyelashes have formed, and at week 27 the baby is gaining fat (Mayo Clinic).
Second trimester fetal development by week range, by source.
How big is your baby? UPMC compares your baby to a peach at the start of the trimester and a cauliflower by 27 weeks. Each number below is printed as its source wrote it, not converted.
Week
Mayo Clinic (crown to rump)
Office on Women’s Health
14
About 3.5 inches (87 mm), about 1.5 ounces (45 g)
Not given
16
About 4.75 inches (120 mm), about 4 ounces (110 g)
About 4 to 5 inches, almost 3 ounces
18
About 5.5 inches (140 mm), about 7 ounces (200 g)
Not given
20
About 6.3 inches (160 mm), about 11 ounces (320 g)
About 6 inches, about 9 ounces
22
About 7.5 inches (190 mm), about 1 pound (460 g)
Not given
24
About 8.25 inches (210 mm), over 1.3 pounds (630 g)
About 12 inches, about 1 1/2 pounds
26
About 9 inches (230 mm), nearly 2 pounds (820 g)
Not given
Baby size by week. Sources measure differently, so both are shown.
Mayo Clinic measures crown to rump, which leaves out the legs, so its lengths run shorter. Boy or girl? UPMC says the genitals are visible by the 20 week scan, and MedlinePlus says it can show the sex if you want to know.
Baby on the way? Get ahead on sleep.
Our free two-minute quiz builds a gentle, personalized sleep plan you can use from the first weeks at home.
The Office on Women’s Health says most women find the second trimester easier than the first, and UPMC says morning sickness, fatigue and mood swings usually fade.
Symptom
What the sources say and what helps
Aches
Back, belly, groin and thigh aches (Office on Women’s Health), plus sore hips (UPMC). UPMC suggests low-impact exercise such as walking or swimming.
Heartburn
On UPMC’s list. MedlinePlus suggests a smaller dinner and no big meal close to bedtime.
Bigger appetite
UPMC lists it. The CDC suggests about 340 extra calories a day.
Skin changes
Stretch marks, darker nipples, a dark line below the belly button, darker facial patches and itching on the belly, palms and soles (Office on Women’s Health).
Swelling
Of the ankles, fingers and face (Office on Women’s Health). Sudden or extreme swelling can signal preeclampsia: call right away.
Numb or tingling hands
Carpal tunnel syndrome, per the Office on Women’s Health.
Leg cramps
MedlinePlus suggests pressing your feet against a wall or standing on the cramping leg.
Second trimester symptoms and what helps, by source.
Feeling your baby move. UPMC says first movements are usually felt around 16 to 20 weeks. Mayo Clinic says you might start feeling movement around week 20, often called quickening.
Body and Belly Changes
Your bump usually shows this trimester, and no two look alike. UPMC links the so-called pregnancy glow to your higher blood volume and lists larger breasts. See pregnant belly by month for a month by month view.
Fundal height. UPMC says providers start measuring around week 24, with a tape from your pubic bone to the top of your uterus, to check growth.
Prenatal Tests and Appointments: Months 4 to 6
MedlinePlus says to expect a visit every month, and UPMC says every four weeks, more often if your pregnancy is high risk. Visits include your weight, blood pressure and often a urine check (MedlinePlus).
Test
Window
Source
Fetal screening, if not done earlier
Around week 14
UPMC
Quad screen, a blood test for the risk of conditions such as spina bifida and Down syndrome. It does not diagnose.
Weeks 15 to 22, most accurate at 16 to 18 (MedlinePlus)
UPMC, MedlinePlus
Amniocentesis (optional), offered when risk is higher
Weeks 15 to 20 (UPMC) or 14 to 20 (MedlinePlus)
UPMC, MedlinePlus
Anatomy ultrasound, about 45 minutes, checks organs, growth, placenta and fluid
Around week 20
UPMC, MedlinePlus
Glucose screening: a sugary drink, then a blood draw an hour later
Weeks 24 to 28
UPMC, MedlinePlus
Antibody screening if you are Rh negative
Possible RhoGAM shot around week 28
MedlinePlus
Second trimester tests and their windows, as read in October 2026.
Vaccines: UPMC lists flu and COVID-19 during respiratory virus season. Guidance changes, so confirm with your provider. Call before you start any new medicine, vitamin or herb, including a change to your prenatal vitamins (MedlinePlus).
Weight Gain and Extra Calories
The CDC says to add about 340 additional daily calories during the second trimester. Its recommended total gain for the whole pregnancy depends on your body mass index (BMI) before pregnancy, using Institute of Medicine ranges:
BMI before pregnancy
One baby
Twins
Underweight (less than 18.5)
28 to 40 pounds
50 to 62 pounds
Normal weight (18.5 to 24.9)
25 to 35 pounds
37 to 54 pounds
Overweight (25.0 to 29.9)
15 to 25 pounds
31 to 50 pounds
Obese (30.0 to 39.9)
11 to 20 pounds
25 to 42 pounds
Recommended total pregnancy weight gain from the CDC, as read in October 2026.
The CDC gives totals, not a weekly target, and says to ask your provider about triplets or more. Your weight is checked at every visit, so ask what pace fits you.
Exercise, Travel and Sex
Exercise. The CDC suggests at least 150 minutes of moderate aerobic activity a week, split however you like, after checking with your provider. UPMC says it is fine to keep exercising, switching to walking or swimming if your back or hips ache, and to avoid heavy lifting or bending that causes pain.
Travel. The CDC says travel is rarely ruled out in a normal pregnancy and that the risk of obstetric complications is greatest in the first and third trimesters. Planning a babymoon? From the same page:
Most airlines allow flying until 36 weeks, some limit international flights earlier,; cruise lines generally restrict travel beyond 24 weeks.
On long trips, drink fluids, walk, stretch and ask about graduated compression stockings, since blood clot risk is higher in pregnancy.
Wear the shoulder strap between your breasts and the lap belt low across your upper thighs, below the belly.
Reconsider travel to areas with a Zika outbreak, and check other destination notices first.
Sex. Mayo Clinic says sex does not harm the baby in a pregnancy without complications and does not cause miscarriage, and most positions are fine if comfortable. Your provider may advise against it if you have vaginal bleeding, leaking fluid, a cervix that opens early, placenta previa or a history of preterm birth. Call for severe cramping that does not ease or heavy bleeding.
Sleep in the Middle Months of Pregnancy
MedlinePlus says sleep often gets harder as pregnancy goes on: finding a position, bathroom trips, heartburn, aches and a more active baby all play a part.
Sleep position. MedlinePlus does not tie its advice to a specific week. It says to sleep on your side, that side lying with your knees bent is likely most comfortable, that many providers suggest the left side, that switching to the right for a while is fine, and that it is best not to sleep flat on your back.
Seek care right away. UPMC lists these second trimester warning signs. Go to labor and delivery or an emergency room if you cannot reach your provider quickly, and call 911 in an emergency:
A severe or persistent headache, especially with blurred vision, nausea, or swelling of your face and hands, which can be signs of preeclampsia.
Difficulty breathing, a racing heartbeat or chest pain.
Severe stomach pain or strong cramps, which can be a sign of preterm labor.
Vaginal bleeding.
Swelling, redness or warmth in one leg, which can be a sign of a blood clot.
A fever above 100.4 F, or pain when you urinate.
Thoughts of harming yourself.
Call your provider for any of these from MedlinePlus: any bleeding; more vaginal discharge, or discharge with an odor; fever, chills or pain when urinating; moderate or severe cramping or low belly pain; and any symptom that worries you, even if it seems minor.
The Office on Women’s Health adds two: itching together with nausea, loss of appetite, vomiting, jaundice or fatigue, and sudden or extreme swelling or gaining a lot of weight really quickly.
If something feels wrong and it is not on a list, call anyway. This article is general education, not medical advice.
Frequently Asked Questions
When does the second trimester start, week 13 or 14?
Both are used. By the ACOG definition, as reported by UPMC, it starts at 14 weeks 0 days. The Office on Women’s Health and Mayo Clinic start it at week 13, and MedlinePlus uses weeks 14 to 28. Your care does not change on that exact day, so follow your provider’s chart.
How many months is the second trimester?
About three and a half months. UPMC says the second trimester lasts about 14 weeks, or 3.5 months, on the ACOG definition. Counting about 4 weeks and a few days per month, it covers roughly months 4, 5 and 6 of pregnancy. Months are a convention, so providers count in weeks.
How many months is 13 weeks pregnant?
About 3 months. Thirteen weeks is 91 days, so you have completed about three calendar months and are starting the fourth. Week 13 is the first week of the second trimester for the Office on Women’s Health and the last week of the first trimester by the ACOG definition.
When will I feel my baby move?
UPMC says first movements are usually felt around 16 to 20 weeks, and Mayo Clinic says you might start feeling movement around week 20, often called quickening. Early movements are light, so ask your provider at your next visit if you have questions about what you are feeling or when.
How much weight should I gain in the second trimester?
The CDC gives totals for the whole pregnancy, not a weekly target. For one baby it recommends 25 to 35 pounds at a normal BMI before pregnancy, with other ranges for other BMIs. It suggests about 340 extra calories a day in the second trimester. Ask your provider what pace fits you.
What should I avoid in the second trimester?
UPMC says to keep avoiding alcohol and other substances, high-mercury ocean fish and foods that carry a risk of foodborne illness. It also suggests skipping heavy lifting or bending that causes pain. MedlinePlus says to check with your provider before starting any new medicine, vitamin or herb, and not to take sleep aids.
Calmer days, better nights.
Betteroo builds a personalized sleep plan for your baby. Take the free two-minute quiz and have it ready before the newborn weeks.
