What have been the biggest advancements in recent obstetrics?

Cell-free fetal DNA . The newest advance that i can think of is the development of a test using the mothers blood sample that can tell with >99% accuracy if the baby has certain chromosomal/ genetic defects. It can be done as 10 weeks of gestation to determine if a baby has down syndrome, trisomy 3 or trisomy 18.
Advancements in Ob. The single biggest advance in obstetrics is ulltrasound. This has allowed detailed anatomical surveillance of the fetus and accurate measurements of fetal growth and well-being.
Genetic screening. There is now available genetic testing that is highly accurate that looks for fetal dna in the mothers bloodstream -commercially available kits include harmony and panorama. This is a huge advancement and at some point will replace more invasive tests like amniocentesis. Most insurance carriers pay for the testing and there are very low false positives and even lower false negatives.
C-section ultrasound. The highly safe performance of the most common life-saving operation in modern medicine namely cesarean section and the evolution of obstetrical ultrasound into ultrasonic obstetrics have transformed perinatology and even created the new fields of fetology and fetal intervention. Add to those achievements the explosion in prenatal genetics and the advent of non-invasive dna analysis of the fetus!