How do twins develop in the womb?

Plus, tips on a how to have a healthy twin pregnancy. By Tammy Jacks

How twins develop

If you’re pregnant with twins, congratulations! A double miracle has just taken place in your belly. Whether the chances of having twins runs in your family, or it’s because of fertility treatments, a twin pregnancy is special and exciting.

ALSO SEE: 10 twin pregnancy symptoms to look out for

How twins are made

Although all of us share 99% of our DNA, the remaining 0.1% is enough to make each of us unique. However, in the case of identical twins, they share 100% of their genes and have the same DNA. In this case, one egg and one sperm have fertilised and split into two separate embryos for twins to develop, explains Johannesburg-based gynaecologist and obstetrician, Mark van der Griendt.

If you’re expecting non-identical or fraternal twins, two separate eggs have been fertilised at the same time by two sperm and these embryos develop separately in the womb, says Dr van der Griendt. Non-identical twins are just like normal siblings, except that they happen to be born at the same time.

Still one of a kind

Studies have repeatedly shown that identical twins have the same DNA, but their mothers can still tell them apart. Why? Because what’s written in your baby’s genes is only half the story. There are many lifestyle and external influences that play a part in how your babies develop. Even identical twins go on to lead separate lives and develop their own, unique character traits, which is often what distinguishes them.

Do twins share the same placenta?

This largely depends on how the eggs are split in the first few days after conception. Non-identical or fraternal twins will always have their own placenta and they’ll develop in their own amniotic sac, says Dr van der Griendt. The placenta will embed and grow along the uterine wall and will provide your little one with essential oxygen and nutrients via the umbilical cord.

With identical twins, it’s more complex. These little ones can have shared or separate placentas. If the embryo is split right after conception, with no delays, then the chances are that they will form and develop much like fraternal twins – with their own placentas. However, if the split is delayed for a few days, the embryos will develop separately, but with a single, shared placenta explains genetic expert and pathologist, Kurt Benirschke. “In most cases, these multiples will be enclosed within a shared chorion (the outer layer of the sac that contains a foetus), but will develop individually within separate amnions (the inner membrane surrounding the sac of amniotic fluid),” he adds. In other cases, twins can also share the placental bed. In other words, two placentas develop right next to one another along the uterine wall and it appears that there’s one placenta, but there’s still two, explains Dr van der Griendt.

Possible risks with a multiple pregnancy

Carrying more than one baby at a time always puts a little extra pressure on the mom-to-be, physically and emotionally. Dr van der Griendt regularly measures his patient’s cervix to ensure that it’s closed and the length is right to carry the babies as far as possible. He also keeps an eye on the amniotic fluid as well as the umbilical cord – especially with identical twin pregnancies where there is an increased risk of the umbilical cord getting tangled around one of the baby’s necks. “These days, most twins are born via C-Section between 36 and 38 weeks, if the pregnancy is relatively low-risk and without complications,” says Dr van der Griendt.

ALSO SEE: What to expect when expecting multiples

Tips to have a healthy twin pregnancy

Dr van der Griendt always advises his patients to eat wholesome, nourishing foods throughout pregnancy, but not to eat for two or three. “Average-size portions, and small regular meals work well,” he adds. It’s also important to drink plenty of fluids, even though you’ll feel the urge to go to the loo often. Staying hydrated is critical for you and your babies.

He also suggests resting as much as possible, and putting your feet up – especially in the third trimester when your little one’s are growing at a rapid rate, and there’s extra strain on your body and organs.

Johannesburg-based primary school teacher and mom of twin boys, Nicola Ellmore, had healthy twin boys who each weighed 2.8kg at birth. She shares her top tips and survival strategies for pregnancy and beyond…

  • If you have prolonged morning sickness and struggle to keep food down, chat to your doctor about safe medications you can take. Your babies need nourishment.
  • Avoid spicy foods if possible. Although some women love spicy food and have grown up eating it, I found that I felt better when I stuck to plain, easy-to-digest foods especially in the first 12 weeks. I also slept better and experienced less stomach cramps and bloating when I ate a simple diet.
  • Go for even more check-ups and scans with your healthcare provider (than the recommended amount with single pregnancies). This helped to ease my anxiety and I was also able to keep track of the twins’ growth and development.
  • Be a part of a supportive community and join the South African Multiple Births Association (SAMBA). They hold regular conferences for parents and answer your most pressing questions (including which prams to buy etc), as well as offer unique tips and advice for multiple pregnancies and successful births.
  • Opt for a night nurse if you can in the first few months. We referred to our night nurse as our Angel. We only had her a few nights a week but this helped to catch up on some much-needed sleep, and I was a calmer, happier mother in the day.
  • Try to incorporate regular, yet gentle exercises into your daily routine. This not only helps to boost blood flow and keep your weight in check, it also helps to ease general aches and pains and alleviate fatigue. I joined a Preggy Bellies class early on and continued twice a week until I was around 30 weeks pregnant.
  • Go on maternity leave early if you can. I stopped teaching from 31 weeks because my gynaecologist was concerned about me being on my feet (as they were swelling quite a bit) and encouraged me to rest more. I really believe that this additional rest helped me to carry my boys until 37 weeks.
  • Stick to comfortable, breathable clothing and avoid anything that’s too tight. I was pregnant in summer and lived in light, cotton dresses and baggy shorts.
  • Get organised early. Because the majority of multiples are born at around 35 weeks, don’t leave things like packing the hospital bag and important documentation until the last minute. You also want to get the nursery ready and buy all the essential items you need when you still have the energy and can drive around! (I had to stop driving when I was 35 weeks because my tummy was just too big).


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