Fetal development of twins month by month, how do twins grow? Renowned medical illustrator Peg Gerrity takes us inside the ᴡᴏᴍʙ to see how fraternal twins develop from the moment of implantation until they’re ready to be born, as detailed by the American College of Obstetricians and Gynecologists.
In three weeks
Nonidentical twins like these (also known as fraternal or dizygotic twins) are the most common. Each baby is developed from another ꜰᴇʀᴛɪʟɪᴢᴇᴅ ᴇɢɢ. By three weeks, each zygote will have developed into a ball of several hundred cells called a blastocyte and is beginning to see itself implanted in the uterine wall.
Twins at 4 weeks
The twins are now embryos, made up of two layers of cells from which all body parts and organs will develop. By next week, the amniotic sac and placenta will have formed for each baby.
Twins at 8 weeks
By 8 weeks, babies already have bendable hands and feet. Their hearts have already been beating for two weeks. Nerve cells in the brain grow to connect with each other.
Twins at 12 weeks
The twins are busy hitting and stretching. Their hands come together on their chests and the little nails start to grow. Eyelids cover their eyes. Tooth buds grow in the gums.
Twins at 16 weeks
Children already have unique fingerprints. They can squirm and start peeing in the amniotic fluid. They can drink and swallow amniotic fluid. You can also see the sex of the babies on ultrasound.
Twins at 20 weeks
Talk to the twins because they will be able to hear you now. Hair is now growing on their buttocks. They have a kind of white fat on their skin that protects them from the liquid environment in which they are.
Twins at 24 weeks
Eyebrows grow. The tooth buds are in place and the taste buds are working too. The skin is red and wrinkled now, regardless of the color of the baby’s skin after birth.
Twins at 28 weeks
Twins can open their eyes and the eyelids already have eyelashes. Fat layers are deposited under the skin, smoothing it. They can suck their fingers and you can feel them when they hiccup.
Twins at 32 weeks
The nails now cover the fingers and toes. The hands, feet, and trunk are developing better and better. Most of the twins will be born in the next few weeks.
Twins at 36 weeks
Most twins are born at 36 weeks. The lungs mature up to 34 weeks, and in the last weeks they gain weight. Most twins are around 2500 g.