16 weeks pregnant

Your baby at 16 weeks

Sixteen weeks is the end of ACOG's 13-to-16 week band, and the changes it lists are mostly about structure becoming firmer. Bones are hardening, especially the long bones of the arms and legs. The skin is still thin enough to see through, though ACOG says it will start to thicken soon. Toenails have formed, the neck is now defined, and the lower limbs are developed. Hearing begins to develop, and the lungs are starting to form the tissue that will exchange oxygen and carbon dioxide once breathing starts after birth.

Fingerprints are still to come: ACOG places the ridges that later become fingerprints and footprints in weeks 21 to 24.

The numbers shown above come from two different rulers. The length, 11.6 cm, is crown to rump, the same measurement a sonographer takes, because the legs are still tucked up. The weight comes from the WHO fetal growth charts (Kiserud and colleagues, 2017), which give an estimated fetal weight, 144 g in the middle at exactly 16 weeks. The 10th and 90th percentiles, 124 g and 166 g, show how far apart two healthy babies of the same age can be. Because the figure is calculated from ultrasound measurements rather than a scale, it carries a margin of error. The same chart puts the average head circumference at 123 mm.

One thing that is special about this week is how little your baby weighs compared with what is coming. On the same chart, the middle estimate is more than four times higher by week 24, so most of the growth in weight is still ahead. For now, the work is shape and function.

Your body at 16 weeks

Many people feel better around now. The first-trimester sickness and tiredness often ease, and your belly may begin to curve outward, though plenty of people still do not look pregnant to strangers.

The NHS lists a routine appointment at 16 weeks. Expect a blood pressure check and a urine test, a look back at any earlier screening results and a word about the scan still ahead, with time for your own questions about how you are. It is a good moment to raise anything on your mind, from work to mood. If your clinic or hospital also offers a cervical length check or other optional tests, the table below shows the window.

This is a sensible time to settle into a routine of gentle movement. The NHS recommends about 150 minutes of moderate activity a week, such as walking, swimming or yoga, at a pace where you could talk but not sing. If you are new to exercise, start with around ten minutes a day and build up.

Common symptoms around 16 weeks

• Back and pelvic aches. The NHS explains that ligaments soften and stretch in pregnancy to get ready for labor, which can strain the lower back and pelvis. Bend at the knees, wear flat supportive shoes, share the weight of bags and try a pillow between your knees at night.
• Heartburn. The NHS links it to hormone changes and to your baby pressing on your stomach, and says it is more common from 12 weeks onward. Smaller meals, sitting upright while you eat and leaving three hours before bed can help.
• Tiredness that comes and goes. The first-trimester exhaustion lifts for many people, but the NHS says you may feel tired again later because of the extra weight you carry.
• Faint flutters. Some people notice a swirling or bubbling feeling for the first time. If you do not, that is not unusual; first-time parents often feel nothing until after 20 weeks.

Tips for this week

• Practice side sleeping. The NHS says the safest position to go to sleep in pregnancy is on your side, left or right. It is easier to build the habit now, while a pillow between your knees is the only fuss.
• Look up antenatal classes. Find out what is offered in your area, when sessions start and whether partners can join.
• Write down your questions. Bring them to the 16-week appointment, along with your maternity notes if you have paper ones.
• Plan for the mid-pregnancy scan. The NHS offers it between 18 and 21 weeks, and ACOG says the standard ultrasound is usually performed between 18 and 22. It is worth deciding now whether you want to learn the sex.
• Keep moving, gently. Choose what you already enjoy, and swap running for brisk walking if it becomes uncomfortable.

When to call your doctor or midwife

Do not save these for your next appointment. Heavy bleeding, severe pain, fainting or shoulder-tip pain are reasons to call your local emergency number straight away. Light spotting or mild cramping should be reported to your midwife or doctor on the same day; before 20 weeks that may mean your early pregnancy unit, or your local non-emergency health line if neither answers.

• Call the same day if you have light vaginal bleeding or spotting with little or no pain, or mild cramping. The NHS says to get urgent help from your maternity unit or early pregnancy unit.
• Call your emergency number if you are bleeding heavily, or if bleeding comes with severe tummy pain, shoulder pain, or feeling sick, faint or dizzy.
• Call now if you have started to feel your baby move regularly and then notice the movements slow down, stop, or change from their usual pattern: ring your midwife or maternity unit straight away. The NHS says not to wait until the next day. The NHS and the RCOG say there is no set number of kicks to count, only what is usual for your baby; if your own care team has asked you to count kicks, do what they advise.
• Call now if sickness has carried on into this week and you have kept nothing down for 24 hours, your pee has turned very dark or you have not passed any in over 8 hours, or you feel faint when you get up.
• Call now if peeing hurts or burns, particularly with a fever or pain in your side under the ribs.
• Tell your midwife if you have not felt any movement by 24 weeks, so they can listen to the heartbeat and check on your baby.