4 weeks pregnant with twins: Twin pregnancy week by week

Read about your pregnancy from week 3+0 to 3+6. You're now 4 weeks pregnant with twins.

By Kate Phillipa Clark

When you’re 4 weeks pregnant with twins, the fertilized eggs reach your uterus.
With fraternal twins, two eggs have been released from your ovaries and fertilized by two separate sperm cells. They will now attach themselves to the lining of your uterus. This is called implantation. Identical twins stem from an egg splitting in two.

What do identical twins share?

If the split happens within the first three days after ovulation, identical twins will have their own placenta, amniotic sac and outer membrane. This is similar to fraternal twins. This is called a dichorionic-diamniotic (di-di) twin pregnancy. If the split happens later the twins will share an outer membrane and placenta. In most cases, they each have their own separate, inner membrane. This is the case for two thirds of identical twins, so it’s the most common type of identical twin. This is called a monochorionic-diamniotic (mo-di) twin pregnancy. It is possible for identical twins to share an inner membrane (amniotic sac) too, but it’s very rare and only happens in about one percent of identical twin pregnancies. This is called a monochorionic-monoamniotic (mo-mo) twin pregnancy.

How are my babies developing?

Your babies (or baby)* are like two tiny balls – called blastocysts – and are already consisting of several hundred cells that are multiplying. The part that will develop into the placenta(s) has started producing the pregnancy hormone human chorionic gonadotropin (hCG). When you’re 4 weeks pregnant with twins, the blastocysts are receiving oxygen and nutrients from their yolk sac(s) until the placenta(s) is ready to take over.

*If you’re having identical twins and the egg hasn’t split yet.

How will my body react?

Some women might notice spotting – or slight bleeding – for one or two days around the time of implantation. This is called implantation bleeding. It happens when the fertilized egg attaches to the inside of the uterus. After implantation, the lining of the uterus gets thicker and the cervix is sealed by a plug of mucus. It will stay in place until the baby is ready to be born.

When does a pregnancy test turn positive?

You might be able to get a positive pregnancy test result, when you’re 4 weeks pregnant with twins, but don’t count on it. Usually it takes 3 to 4 weeks from the first day of your last period for the levels of the pregnancy hormone hCG to be high enough to be detected by pregnancy tests. The pregnancy hormone tells your ovaries to stop releasing eggs. It also triggers increased production of estrogen and progesterone. These hormones keep your uterus from shedding its lining and stimulate the growth of the placenta(s). You won’t ovulate while you’re pregnant.* This also means that you won’t get your period.

*It’s possible for a woman to continue ovulating after becoming pregnant, but it’s very rare. It’s called superfetation, if she becomes pregnant while already pregnant.

What do I need to remember?

Take folic acid. Folic acid is a B vitamin and is standard for pregnant women and women who plan to become pregnant. Folic acid helps prevent neural tube defects. Neural tube defects are serious birth defects of the spinal cord and the brain. You need to take 400 micrograms (mcg) for the first 12 weeks of pregnancy. Ideally, you should begin taking folic acid at least a month prior to you getting pregnant.


Read about next week – week 5


About the Author

Kate Phillipa Clark

Kate Phillipa Clark has a bachelor in Journalism and an Executive Master in Corporate Communication. She is an identical twin and so is her father.


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