Understanding CRL Lag in Early IVF Pregnancies: A Patient Story

Question
QUESTION: I am currently 9w/1d and here is my story:

IVF #1 - m/c, IVF #2 - bfn, IVF#3 - bfp (confirmed on 3/25 -14dp3dt)

At my 5w/4d u/s the re was able to see 2 small sacs. At 6w/4d, both sacs were visable as was a heartbeat, but the sacs were measuring about a week behind. At 7w/4d, both sacs were visiable with a bpm of about 130, and again, both sacs were measuiring a week bihind.

I had mild spotting of dark brown blood at 7w/5d and went in for another u/s on 7w/6d; both babies were visible and h/bs were still at approximately 130 bpm. RE was able to detect a small blood clot behind sac B. He also said that sac B is small for the baby and that he did not feel confident that baby B would make it, but that baby A looked good.

At 8w/5d, babies were still measuirng a week behind with hbs of about 167 bpm (sac B is still small).

My questions are (1) is this common for IVF or twin pgs to be a week behind in measurement (2) should they catch up or could they be consitantly 1 wwek behind for the entire pg and (3) My RE says that he is pleased with the consistant growth, but should I be worried that we are an increased risk of m/c because they are a week behind?
ANSWER: Dear Andrea,

According to an article in BJOG: An International Journal of Obstetrics and Gynaecology, "The gestation sac size in pregnancies resulting from in-vitro fertilization (IVF) and embryo transfer have been compared with those in spontaneous pregnancies. Small-for-dates gestational sac sizes were found in 36% of the IVF pregnancies. This proportion held for both singleton and multiple pregnancies. With increasing gestation beyond 8 weeks the gestation sac volume increasingly approached normal. In contrast to spontaneous conceptions, IVF pregnancies had a low rate of pregnancy loss once fetal heart movements were demonstrated, when the gestation sac size was small-for-dates. Small sac size in an IVF pregnancy may lead to the misdiagnosis of a failed pregnancy."

So - according to this reference, (1) it is fairly common for IVF pregnancies to have small sac sizes, and (2) they do tend to catch up after the 8th week, and (3) the risk of pregnancy loss due solely to a small sac size is greatly decreased once heart activity is visualized.

I hope this information has helped you and answered each of your questions. I wish you well!

Brenda

---------- FOLLOW-UP ----------

QUESTION: Thank you for your help, it was very reassuring!  If at all possible, can you please provide me with the article name, date published and author(s) of the journal article you referenced.

Thanks!

Answer
Dear Andrea,

It was from the British Journal of Obstetrics and Gynaecology:  Volume 92 Issue 9 Page 953 - September 1985. The title of the article was "Gestation sac size in in-vitro fertilization pregnancies" and there were numerous authors as it appeared to be a collaborative effort.

Hope that helps!

Brenda