What Are the Major Steps of Twin Pregnancy Development?

Congratulations! It’s twins! Hearing these words from your obstetrician can be both thrilling and alarming. Carrying not one, but two developing babies can seem like a big job for a mom-to-be. But month to month, there are many exciting stages of twins pregnancy development that result in welcoming two bouncing babies into the world. Read on for more milestones that will occur month by month in a pregnancy.

Twin Pregnancy Development

Twin Pregnancy Development: Month 1

Twins can be identical, meaning they split from the same fertilized egg and share the same placenta, or fraternal, where two separate sperms fertilized two different eggs in the uterus. Fraternal or non-identical twins will have separate placentas because they arose from two different eggs. While most women may not start to experience symptoms associated with pregnancy until weeks 5 to 6 of their pregnancy, women pregnant with twins may notice symptoms earlier. This is because growing two babies can result in a lot of hormones, especially human chorionic gonadotrophin (hCG) hormone. This hormone can unfortunately result in morning sickness where a woman feels especially nauseous in the mornings during her pregnancy.

Twin Pregnancy Development: Month 2

Another sign associated with twin pregnancy development is that an expectant mom may appear larger or further along in terms of her uterus size than when compared to a mom pregnant with one baby. While a mom at two months may not yet be showing signs of pregnancy, her doctor will note that she is larger than is expected. That’s because she is already growing two babies that will have arms and legs that bend. They also have hearts that will start beating at roughly week six of pregnancy.

Twin Pregnancy Development: Month 3

At month three, your babies can suck their thumbs and are starting to develop their genitalia. They also have functioning urinary and kidney tracts. Ideally in the third month of pregnancy, nausea will start to subside as hormones that increased to support the twins’ growth start to regulate and the placenta takes over more of the hormone production functions.

Twin Pregnancy Development: Month 4

During month four of pregnancy, each baby will have his or her own fingerprints. You won’t have to wonder about their gender much longer either! Most babies’ gender can be visualized on an ultrasound by about 16 weeks. If the twins are of different genders, they are fraternal (non-identical) twins. However, if the babies are the same sex, a doctor may not be able to predict at this time if they are identical or fraternal.

Twin Pregnancy Development: Month 5

Moms pregnant with twins can often feel their babies moving at an earlier time compared to women pregnant with only one baby. This may be because there are two babies in there, moving around and making themselves known. At this stage in development, the babies are still small enough that their movements may feel like fluttering. However, as they start to grow larger, the movements will more closely resemble kicking. Your twins are also developing their hearing, meaning they can hear you if you talk to them.

Twin Pregnancy Development: Month 6

By this time, your babies may be growing together so much that they will rub close together. Often, ultrasound imaging will reveal the babies touching heads in the womb, separated by only a thin amniotic sac. During this phase, a doctor will measure the babies carefully, especially their heads, to ensure they both are developing at the same pace. This is because with a twins’ pregnancy, it is possible that one twin could get significantly more nutrition or blood flow than the other.

Twin Pregnancy Development: Month 7

As you near the home stretch of pregnancy, your babies are achieving important milestones that will help them be strong and healthy outside the womb. This includes developing lungs as well as a liver that is maturing. Each babies’ bones will continue to ossify or harden during this time, including the skull bones. Although the pieces of the skull bones will not fuse together until after the babies are born, they are still developing toward this goal.

Twin Pregnancy Development: Month 8

During month 8, the babies have made most of their needed organ developments and are just continuing to grow more and more in preparation for delivery day. At this time, your babies’ body systems are developing and functioning, including being able to pee in the womb. During month 8, it’s important to ensure you have your hospital bag packed because your babies will be delivered soon.

Twin Pregnancy Development: Month 9

According to Huggies, most twin pregnancies will be delivered on or before the 40-week mark that is considered a full-term pregnancy. The most common cause of preterm labor in moms who are expecting twins is simply running out of room. When babies cannot grow any more due to lack of space, a mother’s body may trigger labor. Ideally, you will be far enough along in your pregnancy that you can deliver twins with healthy lungs and organs. According to the Mayo Clinic, most women pregnant with twins will deliver their babies via induction (giving medicines to induce labor) or C-section by weeks 38 to 39 of pregnancy.

Conclusions on Twins Pregnancy Development

Most babies develop in a twins pregnancy in a very similar manner to women pregnant with only one child. However, there are unique challenges to mom and babies in terms of space. You will go to your doctor’s office on a regular basis (usually monthly at first, then bi-weekly or weekly as your due date gets closer) to check on the babies’ development. As your due date nears, your doctor will especially examine the babies for their positioning. If neither baby is in a head-down position, it may not be possible to deliver the babies vaginally. This is why it is important for moms and doctors to talk about the possibility of C-section before a twins’ delivery.


BabyCenter: Twins Fetal Development Month by Month

Huggies: Twin Pregnancy Week By Week

Mayo Clinic: Twin Pregnancy: What Multiples Mean for Mom

Parents: Twins: A Closer Look at Your Developing Babies