A couple thoughts I've had...first, we need to consider that LE has been asking the parents to release their comments strategically based on their profiling of the kidnapper and how they think the pair will respond. I'm imagining them asking her parents to, for example, appeal to SF using things they have discussed with her before (your value as a person is not based on your job, etc. - paraphrased)...and then when that did not seem to flush them out, to appeal to SF by taking a pragmatically negative stance toward her kidnapper and what SF's future with him might hold. I'm just thinking that they are probably not just making statements all willy-nilly, but with some sort of strategy directed by LE.
Another thing I have to contribute is that during the 2nd trimester of pregnancy, regular well-visits are generally only once every 4 weeks. I've utilized 5 different practices for 5 different healthy, uncomplicated pregnancies (long story!) and they have all held roughly the same appointment schedule: 1 appointment before 13 weeks along (verify pregnancy, likely an ultrasound to establish due date); appointments every 4 weeks between 13 weeks and 26 weeks; every 2 weeks between 26 weeks and 36 weeks; and then weekly until baby arrives. Additionally, 2nd trimester visits are mostly just checking in, weight and blood pressure, fundal height measurement, basically a well visit - except for the anatomy ultrasound around 20 weeks, which some women choose to forego, anyway. I do not know if there would be other indications for appointment scheduling because she is 16, but she does not appear to have an underdeveloped body that would theoretically have a harder time carrying and delivering a baby, which is, I guess, a relatively good thing in this bad situation.
All that to say, that she might not have "missed" any prenatal care in the almost 3 weeks she has been gone. YET. If she stays gone, she will. And I do hope that they safely resurface and that she is able to process how bleak her future with him would be. All MOO.