Week 18 of Pregnancy

First trimester weeks

Congrats! During the first trimester, you’re getting used to the idea of being pregnant.

Second trimester weeks

As you enter this second trimester, your body will settle down to pregnancy.

Third trimester weeks

You've reached the third and final trimester and will be heavily pregnant by now.

Week 18 of Pregnancy

You'll find you're gaining weight week by week, which is perfectly normal.

Not all the weight you're gaining is your baby. In fact, most of the increase is because parts of your body, such as your breasts, are getting bigger and your blood volume is increasing. You might want to think about signing up for prenatal classes now because they fill up quickly. They are a great source of information, as well as a good way to make friends and compare notes with other pregnant women.

17 Weeks 2 Days Pregnant

159 days to go...

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Your baby today

Here, the baby's legs are in the typical crossed-legs position. The right arm is on the right side of the image. The limbs and umbilical cord appear to be in a tangle, but the umbilical cord is filled with a jellylike fluid and does not become compressed.

The tiny embryo was once dwarfed by the placenta but now your baby has outgrown it and will continue to do so.

In the early stages of pregnancy, the placenta grew at a far greater rate than your baby. Your baby has now caught up and from now on will be larger than the placenta.

The structure of the placenta will change over the course of the next few weeks as the second wave of cells move into the spiral arteries in the uterus (see You are 14 Weeks and 4 Days). The placenta is currently at its thickest but as it continues to grow, albeit at a slower rate for a time, it thins out.

Your baby's more rapid growth means that at 2.5 oz (70 g) she is now heavier than the placenta and by the time she is full term she will be six or seven times its weight. Nutrients supplied across the placenta provide your baby with energy for growth, but growth is in part regulated by her own insulin production and insulin-like growth factors.

Although your baby has relatively high concentrations of growth hormone, which is responsible for growth after birth, this does not seem to play an important role in her growth during pregnancy.

The baby is in a typical position, curled with feet and elbows bent. The well-developed ear is still a little low on the side of the head at this point, and the baby's blood vessels show up well.