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Trimester 2 · Week 13 of 40

Week 13 of pregnancy: Second Trimester Begins

The first trimester closes and the NT window ends at 13+6. How much weight to gain for your BMI, when Td is due, and what is new for your baby.

Last updated 28 September 2026

What's happening this week?

This week sits on the boundary between trimesters. This site counts week 13 as the start of the second trimester, while some doctors count the first trimester to the end of this week. Either way, many people feel energy returning and nausea fading. The window for the NT scan and double marker closes at 13+6 weeks. It is also a good time to learn how much weight gain is healthy for you and to check your Td vaccine is on track.

Baby's development

Until now the head has made up a large share of your baby's length. From about this week the body starts to catch up, so the proportions look more like a newborn's. The vocal cords and larynx, or voice box, are developing, and the tooth buds for the milk teeth are established in the jaw. The limbs are lengthening and the skeleton keeps getting firmer.

The intestines have finished moving back from the umbilical cord and now sit fully inside the abdomen. From around 12–16 weeks the gut begins to collect meconium, the dark, sticky substance that becomes the baby's first stool. It normally stays in the bowel until after birth. Its presence in the gut is a normal sign that the digestive system is developing.

You may read that fingerprints are complete at 13 weeks. They are not: the ridges are still forming and will not be fixed until mid-pregnancy. The baby keeps swallowing fluid and making reflex and breathing-like movements, none of which you can feel yet. This is also the last week the NT measurement can be taken, because the baby soon grows beyond the size range the test is designed for.

Your baby's size

About the size of a pea pod

7.4 cm

2.9 in · Length

23 g

Weight

Week 13

Gestational age

Typical crown–rump length is about 6–8 cm now, so the 7.4 cm and 23 g shown are mid-range figures, not targets. The weight is an estimate, and healthy babies can sit well above or below the average. The pea pod is only there to give a sense of scale.

Your body this week

Many people notice a real change around now. As hCG falls and the placenta takes over hormone production, nausea and tiredness often ease, and energy and appetite return. Most people with morning sickness feel better by about 13–14 weeks.

Your uterus is now above the pubic bone and growing steadily, and a small bump may start to show, although many people will not look pregnant for several more weeks. As the uterus rises, some people notice brief pulling twinges in the groin, which are usually harmless. Your blood volume keeps rising, and clothes may soon feel tight around the waist.

Weight gain in the first trimester is usually small, and some people lose a little because of nausea. Most of the gain comes in the second and third trimesters, so this is a sensible point to understand what a healthy total looks like for you, before the steadier gain begins.

Symptoms you may notice

Every pregnancy is different - you may have some, all or none of these.

More energy: Tiredness often lifts as hormone levels settle. If you still feel exhausted, breathless or light-headed, ask whether your haemoglobin should be checked, because anaemia is common in pregnancy in India.
Lingering nausea: If you are still being sick, you are not alone: about one in ten people still have some nausea after 20 weeks. Tell your doctor if it is affecting your eating, work or daily life.
Returning appetite: Hunger can come back strongly. Regular meals with a planned healthy snack help you avoid long gaps followed by very large portions.
Mixed feelings about your shape: Seeing your body change can bring pride, worry or both. Focusing on healthy habits rather than the number on the scale helps many people. If worry about weight or eating starts to take over, tell your doctor or midwife.

Medical care and tests

Td (tetanus-diphtheria) vaccine
Routine
Two doses four weeks apart, from early pregnancy
India's programme gives Td to protect you and your baby against tetanus: a first dose early in pregnancy and a second four weeks later. If you had two doses in a pregnancy within the last three years, one booster is enough. India replaced the older TT vaccine with Td in 2018. If you have not started, ask at your next visit.
Last days for NT and double marker
Commonly offered
Until 13+6 weeks
In India the NT window closes at the end of this week; the UK allows the combined test up to 14+1 weeks. If you miss it, a quadruple marker blood test can be offered in the second trimester, though it does not include the neck measurement.
Weight and blood pressure
Routine
Every antenatal visit
In India both are checked at every visit. Your doctor looks at the trend in your weight against your pre-pregnancy BMI rather than any single reading.
Anti-D after bleeding
Only if needed
If bleeding occurs after 13 weeks
If your blood group is Rh-negative and you bleed after 13 weeks, UK guidance offers an anti-D injection. Practice in India varies, so tell your doctor about any bleeding and your blood group.

Tdap, which also protects against whooping cough, is recommended later in pregnancy by FOGSI and is available privately in India; the government programme gives Td.

Nutrition this week

Build most meals on the pattern in India's dietary guidelines: whole grains or millets, a pulse or other protein food, plenty of vegetables including greens, fruit, and milk or curd. This supports healthy gain better than extra helpings of rice or roti.
Keep added sugar low. Mithai, sweetened drinks, packaged juices and biscuits add calories without much else, and the guidelines advise pregnant women to avoid artificial sweeteners.
If you started pregnancy above a healthy weight, cut back on fried snacks, refined flour and extra oil or ghee rather than skipping meals. Dieting to lose weight is not advised.
If you started underweight, or lost weight with nausea, you may need to eat more; ask for your weight to be monitored closely.

Movement and exercise

Regular activity helps keep weight gain within a healthy range, lowers the chance of gestational diabetes and pre-eclampsia, and is linked with less depression after birth.
With energy returning, try adding light to moderate strength work twice a week alongside walking, swimming or cycling on a stationary bike, building up slowly.
Warm up, cool down and keep cool; exercising in the midday heat is best avoided, and keep water close at hand.

Things to keep in mind

Weigh yourself at about the same time of day, every week or two, rather than daily; day-to-day changes mean little.
Well-meaning relatives may press extra ghee and sweets on you. It is fine to thank them and stick to balanced meals.
If you missed the screening window, do not panic; ask about the second-trimester blood test and the anomaly scan at 18–22 weeks.
Feeling better is a good moment to plan the months ahead, including antenatal appointments and work arrangements.

When to contact your doctor

Call your doctor or midwife the same day if you have

Any bleeding from the vagina, even if light.
Vomiting that continues and stops you keeping fluids down.
Stinging when you pass urine, or needing to go urgently.
A temperature of 38°C or more.
Pain, swelling, warmth or redness in one calf.

Get emergency care now if you have

Heavy bleeding, or bleeding with severe abdominal pain.
Fluid gushing or leaking from the vagina.
Regular, painful cramps or tightenings.
Sudden chest pain, breathlessness or coughing up blood.
Thoughts of harming yourself or feeling unable to stay safe.

In India, call 108 for an ambulance, 102 for free transport for pregnant women in many states, or 112 for any emergency - or go straight to your nearest hospital with a maternity unit.

If something feels wrong, trust that feeling and call - you never need to wait for your next appointment.

Questions to ask your doctor

What is a healthy total weight gain for my BMI?
Are my Td doses complete, or do I need another?
If I missed the NT scan, what screening can I still have?
What is my blood group, and does it matter if I bleed?

Week 13 checklist

Confirm screening is done or booked before 13+6 weeks
Check your Td doses on your MCP card
Note your pre-pregnancy weight and BMI
Start tracking your weight every week or two
Swap one sweet snack a day for fruit or nuts

Frequently asked questions

How much weight should I gain in pregnancy?

It depends on your weight before pregnancy. India's ICMR-NIN guidance, which uses Asian BMI cut-offs, suggests about 10–12 kg in total if your pre-pregnancy BMI was 18.5–23, and no more than about 5–9 kg if it was 23 or above. If you were underweight, you may need to gain more. Other guidelines use different ranges, and your doctor will tailor the target to you.

Is week 13 the first or second trimester?

Definitions differ slightly. This site counts weeks 1–12 as the first trimester and weeks 13–27 as the second, while some doctors count the first trimester to the end of week 13. It makes little practical difference. What matters more is the timing of specific tests, such as the NT scan, which must be done by 13+6 weeks.

I have hardly gained any weight. Is that a problem?

Little or no gain in the first trimester is common, especially if you have had nausea, and some people lose a little. Most weight is gained later. On average, women in India gain less than recommended, so if you have lost a lot, cannot eat much or started pregnancy underweight, tell your doctor so your weight and diet can be reviewed.

This page is general information, not a diagnosis or a substitute for care from your own doctor or midwife. Pregnancies differ, and timings here are typical ranges rather than deadlines. Read our medical disclaimer and editorial policy.