My twins had two placentas, so I don't have personal experience to offer you, but I do know that there are serious risks when a placenta is shared. In particular twin to twin transfusion syndrome (TTTS). This is where one twin gets more blood and nutrients than the other, putting both babies at risk.
At this point, IMO, it is probably better to keep the regularly scheduled US appointments because the risk of TTTS is far greater than exposure to US. In the US they'll be able to see if one baby is getting more blood supply than the other.
Here's the wiki page, hope this helps! PS I'm sure your babies will be perfect!
Congratulations!! It sounds like we are due fairly close together. I am 23 weeks. My twins have separate placentas, which was still able to be determined at my 19 week U/S, so I don't have much relevant info to add. I, too, am leery of U/S exposure, and was able to negotiate with my care provider to have fewer scans. I do think it is important to know if your twins have any shared circulation, so hopefully once that is determined you will be able to make a more informed decision about how many scans would be appropriate in your case.
Mom to eight!! Our twin girls arrived 3-3-2011.
If they share a placenta, they are likely mono-chorionic twins, and they need to be monitored more closely. My girls were mono-chorionic and they had many ultrasounds....extended ones...I had them every two weeks up to 28 weeks and then weekly afterwards. The risk is Twin to twin transfusion, if they detect it, sometimes they can do something about it. My girls are now almost 4 and have met every milestone...they were born at 37 w, 3 days.
I wish I had more time to write now, but I know if you search twin to twin transfusion here, you will find lots of great information.
My opinion is, modern medicine has its uses, and we should utilize them.
Hope this helps.
First, I want to reassure you...it is the 1st trimester scan that would have seen nothing regarding whether or not there was truly 1 placenta. The 2nd trimester or something called a level 2 u/s is what can *sometimes* see if there is one placenta. So actually, you did not miss your chance to see that.
Yes, it is true that TTTS is a risk for MZ twins that share a placenta. However, you must keep in mind that even amongst MZ twins, TTTS is *extremely* rare. If you choose not to monitor via u/s, then you need to pay very close attention to anything that feels like you have rapidly growing amniotic fluid (namely, pain and obvious swelling). When they monitor you for TTTS, they are paying the most attention to size discordance AND fluid levels. (In TTTS, because one twin is donating blood to the other, they have less fluid and nutrients to process and pee out and create amniotic fluid, while the twin who is donated to will have too much because their system is overtaxed.)
I know that there is a lot of scary info out there on u/s. All I can share with you is my experience--and that is, my twins who underwent u/s 3-4 times a week from week 20 to week 36 are both highly capable (intellectually) and are normal children otherwise. OTOH, since the TTTS that they had was just below the qualifying cutoff from the surgery, we had no intervention, so technically it would have been "fine" not to have all those u/s. I would NEVER EVER presume to tell a mother what she should do as far as risk assesment for her children in the womb. For us, because the TTTS was severe and early on while not quite rising to the level of in-utereo surgery, but close enough that both of their lives could have been in danger at any time were it to shift just a bit, we felt that we were willing to risk the potential problems with u/s vs. less timely intervention if necessary and the probable death of both infants (my donor twin was receiving a share of the nutrients that was just abouve the survivability level--we are very lucky that he did not die, and had he, his brother would have either died as well or suffered permanent brain/body injury). BUT....you *must* keep in mind that most MZ twins do not and will not develop TTTS. And many cases of TTTS are not as severe as we suffered through. The earlier it is spotted, the worse the prognosis (Ours was detected at 22 weeks, which is not good). I would say if there was no size discordance at your 2nd trimester scan, and one twin was not severely deficient in fluid, you are probably going to be fine.
I think it is worth it to seek out a qualified, expert opinion and assessment (probably with a perinatologist), at least once though. The average OB/GYN office is *not* equipped to inform you about TTTS, most OB/GYNs operate with extremely outdated and even dangerous information. If you are assessed and they do find significant fluid differences and blood flow problems, I highly recommend starting with www.tttsfoundation.org FIRST. As well as getting a second opinion if you can. There is a lot of horrible information out there, but the TTTS Foundation is internationally respected and has great info, they even educate doctors.
If TTTS is not an issue (and it more than likely will not be), then while you will receive a lot of pressure for stress tests after week 34, I think as long as you are willing to go with your gut and be sure to pay attention to any warning feelings YOU might have, then you will be find to refuse u/s that you don't want. But I guess I would really encourage you to get a real assessment *first*, by a doctor and tech who know what they are talking about. If you were indeed told that you missed your chance to find out if the placentas are separate because you didn't get a first trimester u/s, you are not getting knowledgable or competant advice.
Chiming in late - congratulations on your double blessing!
We discovered we were having twins at a US at 10 weeks. By the time I delivered, I'd had 9 more. My sons were born at 39 weeks, perfectly healthy and normal. They are 16 years old now, Juniors in high school. They don't have any problems that could be associated with high exposure to ultrasound.
I know that I got a lot of comfort every time I saw my babies on US. I believe that the advantage of reducing some of Mother's stress, by closely monitoring the babies and making sure everything is OK, outweighs the possible risks of US.
Best wishes to you for a long and comfortable pregnancy, and two healthy babies!
If the chips are down, the buffalo is empty.