What is different about a twin pregnancy?

In many ways, a twin pregnancy is like a single-baby pregnancy. Healthy twins develop like a single baby does until the last trimester, when their growth slows down. Twins are usually born before the usual 40-week due date.

Carrying twins can be more difficult than carrying a single baby. And the risks are higher for pregnancy problems. That's why keeping up with prenatal checks and tests is especially important.

How do twins grow?

Twins develop from embryos to babies like a single baby does.

• By weeks 10 to 14 of your pregnancy, one or two placentas have formed inside your uterus. It is possible to hear your babies' heartbeats with a special ultrasound device. Your babies' eyes can move. Their arms and legs can bend.
• Around weeks 14 to 18, hair is beginning to grow on your babies' heads.
• By 18 to 22 weeks, your babies can now suck their thumbs. Around this time, you may start to feel your babies move. At first, this might feel like fluttering or "butterflies."
• Around week 26, your babies can open and close their eyelids. You may notice that they respond to the sound of your voice. You may also notice that they do less turning and twisting and more squirming.
• Up to 32 weeks, twins grow rapidly. By this point, they really start to look like babies, with hair and plump skin.
• Around 32 to 34 weeks, twins' pace of growth slows down. Their lungs become more ready for breathing. Babies born after 34 weeks are less likely to have breathing problems after birth.

What can you expect during a twin pregnancy?

You may have the same symptoms during a twin pregnancy that you'd have during a pregnancy with one fetus. But with twins, you may also have earlier and more intense symptoms from pregnancy, like morning sickness, swelling, heartburn, leg cramps, bladder discomfort, and sleep problems. Your belly may grow bigger, and you may gain more weight, sooner. Talk to your doctor or midwife about how much you might expect to gain.

When you're carrying twins, you and your babies may be tested and checked more than you would for a single-baby pregnancy.

• At about 10 weeks, an ultrasound can show if the babies are growing in the same amniotic sac. If they each have their own sac and their own placenta, twins have the best chances of both growing well.
• Between weeks 18 and 20, an ultrasound may be able to show the sex of your babies.
• Later in your pregnancy, you will start to have checkups more often. This will be sooner than for a single-baby pregnancy.

Twins tend to be born early, but 38 weeks is a goal when you and the babies are doing well.

As you get closer to delivery time, your medical team will help you know what to expect and what to do. As questions come to mind, keep a list so you can remember to ask your doctor or midwife.