Finding out you’re expecting twins is quite the
My (Possibly) Identical Twin Pregnancy
I, like many moms, found out I was expecting twins at 8wks of pregnancy. At my first routine appointment, my OBGYN performed an ultrasound and announced there was not one, but two babies, how exciting! After I had picked my jaw up off the floor I asked “Are they identical?”, to which I was told it was too early to tell.
My next appointment at 12wks was a quick drop in appointment and the last with this particular OBGYN. I was about to move, from Texas to Arizona, and although an ultrasound was performed, it was a speedy look in and I was happy just to see two healthy heartbeats. “They’re probably fraternal and you’ll likely give birth around 36-37wks.” he casually said as he shook my hand and left. I was so shocked that I had just lost a week of pregnancy prep (I hadn’t even considered premature birth) that I didn’t ask anything else.
Between a trip to Europe and moving house to Phoenix, it was another 7weeks before I got to see my babies again. “Your previous OBGYN has noted them as fraternal but I don’t see two placentas.” said the ultrasound technician. “Were the placentas looked at during your last ultrasound?” I explained that my last appointment had been a quick one and there was no specific measurements or conversation about the placenta.
A detailed inspection of the placenta was carried out, carefully looking for a tiny junction between two potential placentas. Maybe they had fused? Maybe they were just really squashed up together? Maybe my records were wrong and I was actually carrying identical twins sharing one placenta? I was informed there really was no way to be sure because they were both boys and I had missed the window to confirm one or two placentas. I would just have to wait and see!
I was treated as if they were Mono/Di twins (one placenta, two sacs) because
How to Know for Sure You’re Having Identical Twins:
- During an ultrasound, a single gestation sac is clearly identified. (Mo/Mo twins).
- During a first trimester ultrasound (usually 10-12wks), one placenta is clearly identified. (Mo/Do twins).
Although a single placenta and separate sacs (Mo/Di twins) are usually identical, the window of time to identify a single placenta is small. Around 40% of fraternal twin placentas fuse into one, usually around 13-20 weeks.
How to Know for Sure You’re Having Fraternal Twins:
- During a second trimester ultrasound (usually 16-20wks), your babies are identified as different sexes.
Because I know someone will pull it out of the bag… there have been a handful of reported cases of genetic mutations in male identical twins, causing one of them to lose a Y chromosome and be born a female. Less than 10 cases of this have been confirmed. It’s extremely rare but Mother Nature can be wacky sometimes.
When You Don’t Know if You’re Having Identical or Fraternal Twins:
- Two placentas are identified but the babies are the same sex. 25-30% of twins with two placentas (di/di twins) are in fact identical. The egg would have split very early on and allowed them to implant and grow separate placentas.
- If you did not have an examination of the placenta(s) during your 12wks appointment and two gestational sacs are identified. As the placenta(s) grow it becomes difficult to know if you started with one or two.
How to Find Out if Your Twins are Identical after Birth:
- When your babies are born the hospital should check their blood type. If they have different blood types, they are fraternal.
- A twin zygosity DNA test. Similar to those ancestry DNA kits, you can send off some of your twins’ DNA in the mail and quickly find out if they are identical. Identical twins share 99.9% of their DNA, with natural mutations making up tiny differences.
Going back to those ancestry DNA kits… I recently met a man at the local children’s museum who was reminiscing as my boys were playing. He told me he was also an identical twin and we chatted for a short time. Turns out he had done a ’23 and Me’ DNA ancestry test but laughed when his twin brother’s kids did the same test and he was connected to them as the father… awkward, ha! The magic of matching DNA!
Whether you’re expecting boys, girls, identical or fraternal, I wish you all the best for a happy healthy pregnancy!