Your Pregnancy Week by Week: Weeks 13-16

Medically Reviewed by Traci C. Johnson, MD on March 16, 2023
4 min read

Baby: Your baby is growing quickly! Eyes are moving into position, the ankles and wrists have formed, and though the head is still disproportionately big, the rest of the body is starting to catch up. This week, your baby's intestines are back inside where they belong. Your baby swallows amniotic fluid and absorbs it into their body. Baby's backbone can flex, making large movements easier.  If you think you may be having twins, an ultrasound this week may confirm it!

Mom-to-be: You may have more energy and feel your best these next couple of months. Your uterus has grown a lot. It's filling your pelvis now and starting to grow upward into your abdomen. It probably feels like a soft, smooth ball. If you haven't gained any weight yet because of morning sickness, you'll begin to know as you start to feel better. You may feel a stretch in your belly as your round ligaments stretch. As you begin your 2nd trimester, your risk of miscarriage drops. If your gums swell and bleed from hormones, try a softer toothbrush.

Tip for the Week: Suggest that your partner go with you to a check-up. They might love the chance to hear the baby's heartbeat.

Baby: Your baby's ears are shifting from the neck to the sides of the head, and the neck is getting longer and the chin more prominent. Facial features and unique fingerprints are all there. Your baby is beginning to respond to outside stimuli. If your abdomen is poked, the baby will try to wriggle away. The baby swallows amniotic fluid and passes it as urine. They still have room to float around your womb. Your baby's spleen will take over the development of red blood cells. From head to rump, your child is about the length of a bell pepper -- 3.5 inches.

Mom-to-be: You're probably wearing maternity clothes now. Your skin and muscles are starting to stretch to accommodate your growing baby. You may notice some constipation, because pregnancy hormones relax the bowel. You may salivate more. Tell your doctor if it's a problem. Small spider veins may appear on your legs or face. They will fade after delivery. Small spider veins may appear on your legs or face. They will fade after delivery.

Tip of the Week: Try to ease constipation by getting moderate exercise, drinking plenty of fluids, and eating lots of fruit and vegetables.


Baby: Your baby, from head to heel, is as long as a large russet potato -- 6.25 inches. They're covered by very fine hair, called lanugo, which is usually shed by birth. Eyebrows and hair on the top of the head are beginning to grow, bones are getting harder, and the baby may even be sucking their thumb. Their organs are fully formed now and will continue to grow. You may be able to tell the baby's sex this week with high-resolution ultrasound!

Mom-to-be: Your uterus can probably be felt about 3 to 4 inches below your navel. Sometime in the next five weeks you'll be offered a blood test called the quadruple marker screening test to help screen for Down syndrome. You can talk with your doctor about what prenatal tests you may want. If you're feeling better, you may be more interested in sex. You've probably gained about 15 lbs. on average. You'll start gaining more weight now -- about 1-2 lbs. a week.

Tip of the Week: Start learning to sleep on your left side -- your circulation is better that way. You can try tucking pillows behind you and between your legs. Some pregnancy pillows support your entire body.

Baby: You may be able to hear the baby's heartbeat in the doctor's office. Fine hair, lanugo, may be growing on the head. Arms and legs are moving, and the nervous system is working. Your baby can make slow eye movements behind still-closed eyelids. Your little one can move even more, flexing arms and legs! Bones harden; calcium makes them appear bright white on the ultrasound. Your baby, from head to heel, is the length of a carrot -- 7 inches.

Mom-to-be: Within the next few weeks, you may start to feel your baby move, called "quickening." It often feels like a gas bubble or subtle fluttering movement. As it happens more regularly, you'll know it's your baby. Your body is changing in many other ways. Increased blood volume to support your growing baby may produce nosebleeds, and you may notice your leg veins are becoming more apparent. Good news: Because your uterus is shifting, you may not have to urinate so much.

Tip of the Week: If your leg veins bulge, you may want to wear support stockings, put your feet up when you can, and exercise to improve blood flow.

Your baby's fingers and toes are well-defined; their eyelids, eyebrows, eyelashes, nails, and hair are formed. Teeth and bones become denser. Your baby can even suck their thumb, yawn, stretch and make faces.

The baby's reproductive organs and genitals are now fully developed, and your health care provider can see on ultrasound if you are having a boy or a girl. You don't have to find out the baby's sex yet -- that's up to you.