I am a midwifery student in Canada. As many countries have an average age of first time mothers greater than the USA I agree that you can't nail this down to advanced maternal age. I wonder to what degree income inequality and poor midwifery care contribute.
I have heard that in the USA some midwives charge very little for care and provide home birth services without adequate risking out, back up obstetrical care, and disincentives to transfer care to hospital. For this reason women seeking midwifery care in the USA may choose a poorly trained practitioner and they are much more likely to suffer neonatal and maternal morbidity and mortality.
Personally I think the USA needs better regulation and training of midwives. High school graduates who take an online course and lack hospital privileges shouldn't be delivering babies. I have no idea what proportion of American women seek out this care, however.
If you look at the populations impacted by increasing maternal mortality it seems to boil down to income inequality. When I was a first time mother, I was young and poor. In order to get to my prenatal appointments I had to take an hour long public transit ride to get there. I often waited hours to see my doctor for a 5 minute appointment. By the end of my pregnancy I was skipping appointments right and left. I wonder if low income women in the USA have similar predicaments with access to care, even if they are covered by government insurance for those living in poverty.
I do also wonder about the impact of high c-section rights. I know that's an annoying, stereotypical thing for a midwifery student to say. But according to consumer reports, some hospitals have a c section rate of more than 40% of low risk primips. http://www.consumerreports.org/doctors-hospitals/your-biggest-c-section-risk-may-be-your-hospital/ That seems excessive. And those are just the ones who report their data. c section is obviously a life saving marvel of modern medicine, and I know very little about American medicine, but I wonder why some hospitals have such high caesarean rates on low risk women.