In any pregnancy, but particularly in a twin pregnancy, a lot of development is taking place in your womb. The womb provides a secure place for the babies to grow that is conditioned to meet their needs. There, babies grow from embryos to fully formed infants, responding to pokes, prods, sounds and even the food you eat. Let's look specifically at twins in the womb.
Twins develop when one zygote – a fertilized egg – splits into two parts, forming identical twins, or when two eggs are released and fertilized separately, resulting in fraternal twins. Twin pregnancies are full of new challenges and fascinating facts that make them different from singleton pregnancies in more ways than one.
Let’s take a closer look at four fascinating things that take place for twins in utero.
Twin babies first develop their sense of touch at around seven gestational weeks, at which point in time their mouths become able to feel sensation. About two weeks into your second trimester, your babies’ heads will become more sensitive to touch. Later on in your pregnancy, your babies will be very aware of touch, responding to pressure applied to your baby bump.
Around the start of your 5th month of pregnancy, your babies will start being able to hear sounds. At first, the sounds will be very indistinct to them, muffled by their fluid surroundings as well as the sounds made by your stomach and heartbeat. Toward the end of your pregnancy, your babies will begin responding to external sounds with movement, especially words and phrases that have been repeated when talking to them in utero throughout the pregnancy.
Though it may seem hard to imagine, your babies will be able to smell the things you smell as well as what you eat via the amniotic fluid that surrounds them. Though it doesn’t seem to affect babies in any notable way, the scent is an important sense to them after birth and is what enables them to identify their mother.
As twins develop together, studies have shown that they form a social bond that includes reaching out for one another and touching each other, a demonstration of the inherent impulse to make contact with other humans. This early bond may explain why twin babies are often extremely close, even developing their own imperceptible languages as they grow.
In this documentary by National Geographic assessed the development of twins in the womb, explaining the growth process of twins in utero to fully formed baby. Around 12 or 13 weeks, twin babies take on a more human appearance, and their head and body size becomes more proportional. The first ultrasound happens around this time, and the presence of one or multiple placentas can help a tech identify whether a woman is having identical or fraternal twins.
Later in pregnancy, 3D ultrasounds have shown that babies respond with facial expressions to the ministrations of those manipulating their position in
In one case, twin girls born in the rare condition of both a shared placenta and amniotic sac emerged from the womb holding hands. This beautiful moment was unusual to capture, but not a far cry from the norm from twin babies, who rely on a sense of touch to get to know their sibling from early in the developmental process.
In another case, twin girls were born premature, and one twin was barely hanging onto life after a few weeks. Doctors and nurses made the unprecedented choice to put the healthier twin in her sister’s incubator, where the healthy twin wrapped her arm around her sister. This eased her breathing and helped to restore her vital signs to a normal level. Over a decade later, both girls are still healthy.
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Very young twin babies sometimes react to environments that mimic the womb by curling up against their twin just as they did in that small space. One video demonstrated that twin babies carefully submerged in warm water with their faces exposed to air snuggled with one another and slept, inevitably due to the similarity the situation shared with the conditions from when they were twins in the womb.