To back up a bit: I had a 36 week growth scan on Tuesday and saw the obstetric and diabetes teams. The scan looks fine. Zarquon is consistently on the 50th percentile line and doesn't look to be getting too big or too fat round the middle. I've done a good job with keeping my blood sugar under control, but need metformin over night. It's because of the need for medication that I'm being induced early. If I were well controlled on diet alone, I could probably go to 40 weeks. I think this explains the disparity between the first and second obstetrician I saw. At the time I saw the first one, I was controlling my blood sugar by diet alone, but by the second I'd started on metformin.
It's quite hard finding good information on why early induction is better for GD. The NICE guidance, as far as I understand it, looks at the numbers of early inductions (typically 38-39 weeks) and the outcomes but doesn't really address the underlying reasons for early induction. It's more a case of this is what happens and it seems to be safe. A relevant passage says:
"The NICE induction of labour guideline recommended that women with pregnancies complicated by diabetes should be offered induction of labour before their estimated date for delivery. Although the guidelines reported that there were insufficient data clarifying the gestation-specific risk for unexplained stillbirth in pregnancies complicated by diabetes, the GDG [Guideline Development Group] that developed the induction of labour guideline considered that it was usual practice in the UK to offer induction of labour to women with type 1 diabetes before 40 weeks of gestation."
Early induction for macrosomia (baby over 4kg or 4.25kg depending on who's defining it) is the most commonly cited reason, because of the associated risk of shoulder dystocia. That doesn't seem to be the case for me and Zarquon. There is still a risk of still birth (one study found a rate of 26.8 stillbirths per 1000 live and still births for women with all types of diabetes, not just GD, versus a national rate of 5.7 per 1000 live and still births), although it's unclear if it's actually a larger risk for well-controlled GD.
I have the impression if I ask an obstetrician pointblank why I should be induced early, they're either going to say "because that's standard practice for GD" or say something about the increased risk of still birth, which is probably scary enough for most women to agree to an induction on that basis. But I need to remember I am not an expert at interpreting scientific evidence and medical guidance.
Anyway. I am being induced at 38 weeks or soon afterwards. I am OK with this. I'm not completely convinced it's necessary, but I'm willing to trust the obstetricians' judgement. It did help that the last obstetrician I saw was helpful and friendly, explained why the previous two gave different answers and gave me a thorough explanation of the process of induction, with all of its if-thens and what happens if steps.
Of course, I'd love to know how long it will take to get labour going, but that really is something no-one can tell me. It all depends on how I respond to the drugs. I'm hoping it's fairly straightforward, that the prostaglandin pessary and gels work for me and I don't need syntocinon to get things going. I will have continuous fetal monitoring. I may need a glucose and insulin IV once I'm in labour if my blood glucose doesn't stay in my target range. I'd like to get through labour with my TENS machine and gas and air, but I'm open to the idea of an epidural if I need one. Especially if I do have to have syntocinon. I think I'm more open to having an epidural than to pethidine, because the latter seems to have more side effects for the baby. All these unknowns! And I might still manage to go into labour spontaneously, you never know. We will find out soon.