Your Twin Pregnancy: Week 18 to 20

  • By: Sandra
  • Date: March 18, 2022
  • Time to read: 3 min.

Congratulations, you’re halfway there…well, almost. Since Week 37 is considered full term in a twin pregnancy, by Week 18 you are just about halfway through with your journey. Hurrah!

Fully Formed Babies in Week 18

So what’s going on inside your body right now? Well, at Week 18, your babies are fully formed and are approximately five inches long, and weigh close to five and quarter ounces each, while at Week 20, they will measure about six inches long and weigh nearly nine ounces each.

That’s a pretty significant increase in two weeks but there’s still plenty of growing to do. At this point in your twin pregnancy, you should be gaining about one pound a week. By the time the third trimester rolls around, though, that should increase to a pound and a half. Whew, that’s a lot of weight but you can do it!

Honeymoon Stage of Twin Pregnancy

At this halfway marker, you are also entering the “honeymoon” stage of your twin pregnancy—your morning sickness is finally a thing of the past, and you are still able to move around with relative ease. But that won’t last for long so try to enjoy these few fleeting weeks of mobility. Your appetite should increase now, too, which is great because it’s time to pack on those pounds if you want your babies born big and healthy. 

Remember to concentrate on protein—lean meats and fish—as the amino acids found in protein are essential in building cells and vital in the growth and development of fetal heart, brain, tissue, and muscle. It’s what puts the weight on both you and subsequently your babies. So eat up!

Anatomy Scan at Week 18

Week 18 is also the time when you should have scheduled an anatomy scan or level 2 ultrasound to evaluate the health of both your babies. It takes about 30 to 45 minutes and is pretty standard stuff: With the help of ultrasound technology, the technician or doctor will measure the growth of each baby’s head, femur, and abdomen, checking for abnormalities. He or she will also evaluate the four chambers of the heart, kidneys, lungs, liver, and spine.

Furthermore, the technician will determine if you have the right amount of fluid in your amniotic sac(s), an important factor for moms carrying identical twins as too much or too little fluid could signal a problem such as twin-to-twin transfusion syndrome (TTTS).

And finally, depending on the position of your babies in your uterus at the time of the exam, the technician may be able to determine the sex of each twin as well.

Check Iron Levels

Meanwhile, during this month’s office visit, your doctor will check for anemia as moms carrying twins are more prone to the condition than moms of singletons. No worries, though, as the fix is a simple one—iron supplements. (One sour note here—iron supplements are notorious for causing constipation.)

As long as you aren’t experiencing any complications, the rest of the visit should be pretty routine. You know the drill—you’ll get weighed, your belly measured, your blood pressure taken, and then you’ll be asked to pee in the cup!

Feeling Babies Movement

Moms expecting twins finally get a payoff for all their hard work right around Week 18. For this is about the time that you’ll feel your babies moving (quickening). When the kicking action begins, it’s great fun to try to guess which body part is banging against your stomach lining, or worse, pushing hard against your cervix (ouch!).

And with two babies going at it, some moms find it very uncomfortable. The best way to make them stop all the fussing about? Go for a walk. Slow, gentle movement will quickly put them to sleep.

Register for Childbirth Class

Finally, you’ll want to register for a childbirth class around Week 20, with sessions starting no later than Week 24. Why so early, you ask, especially since women carrying singletons usually wait until their third trimester to enroll? Women expecting twins deliver early or are often put on bed rest. If you schedule your childbirth classes too late in your pregnancy, you may just miss out on all the fun so it’s better to complete the course sooner rather than later.