I had this too, just this past spring! I was really worried as well, so I totally feel you. It was detected at around 12w and at my 20w scan I was told it had resolved itself entirely. I had a few more growth scans to monitor but baby ended up measuring fine. Like a previous poster, I was with the GW midwives and this issue was not considered a major complication and did not warrant referring me out of the midwives’ care and into the OBs practice. Baby was born last month and is healthy and thriving and was a decent weight for her gestational age at birth. OP, sending you good vibes!

Op here. Thanks for the replies. This is my 3rd pregnancy and I have not had this before. I actually have a history of large babies (over 9 lbs) so they were hoping to do growth scans no matter what. Will try and relax about this!

I had this with DS. And by a later scan, it had "corrected" itself, meaning that it was still off-center but not enough to be a concern.

I had a very challenging delivery, where he ended up stalled mid birth canal with HR decelerations that were likely due to cord compressions (his cord was wrapped around his neck). My mom is a neonatologist, and she said that the marginal cord might have contributed to there being a little longer cord to make this happen...though the bigger contributing factor was probably the anterior placement of my placenta.

I tell you this not to scare you (DS and I are both fine...and he was delivered vaginally) but to let you know that it is a good thing to have the OB monitor this since it can impact your delivery.

I had this and they did three additional scans (about once a month after the anatomy scan). They basically are just tracking growth of the baby because it indicates that the cord is still receiving nutrients. Also, I think they might be monitoring to make sure it is still staying attached as everything grows.
FWIW, I was with the GW Midwives and it is my understanding you are referred out of their program if you have any serious medical concerns and this clearly didn't fall in that category for them. This was 7 years ago but I don't remember it being mentioned at appointments very much or raising any concerns with them.

I had this too - it was similarly mentioned somewhat offhand (she described to me what it was but didn't seem concerned) and I subsequently forgot I had it for most of the pregnancy and definitely forgot it afterwards until I read your post. I did have a lot of high-tech scans (twins) and I'm sure they were keeping an eye on this as far as growth/blood flow/etc., but it was never discussed again after that first appointment where we noticed it.

My OB mentioned off hand that my anatomy scan had a note that said my umbilical cord was marginal cord insertion. She made it seem like no big deal and not to worry but if course I am worried lol. I had the scan done at 18 weeks 2 days. She indicated that as the placenta grows the cord insertion could correct itself. Does anybody have any insight into this? Baby is otherwise healthy and at the appropriate weight and size. Will have follow up growth scan at 32 weeks and again at 36 weeks.