Persalinan PretermEtiologi Maternal-fetal stress As discussed earlier, the last trimester is marked by rising maternal serum levels of placental-derived corticotropin-releasing hormone (CR!" #his hormone $orks $ith adrenocorticotropic hormone (AC#! to increase adult and fetal adrenal steroid hormone production, including the initiation of fetal cortisol biosynthesis" Rising levels of maternal and fetal cortisol further increase placental CR secretion, $hich develops a feed-for$ard endocrine cascade that does not end until delivery (%ig" &'-'(, p" )&*!" Rising levels of CR further stimulate fetal adrenal dehydroepiandrosterone sulfate (+EA-,! biosynthesis, $hich acts as substrate to increase maternal plasma estrogens, particularly estriol" -terine +istention #here is no doubt that multifetal pregnancy and hydramnios lead to an increased risk of preterm birth" .t is likely that early uterine distention acts to initiate e/pression of contraction-associated proteins (CAPs! in the myometrium" #he CAP genes that are in0uenced by stretch include those coding for gap-1unction proteins such as conne/in )2, for o/ytocin receptors, and for prostaglandin synthase" Recent reports suggest that gastrin-releasing peptides (3RPs! are increased $ith stretch to promote myometrial contractility and that 3RP antagonists can inhibit uterine contractility .nfectionsPreterm Premature Rupture of Membranes Multifetal 3estation Pan1ang ,erviks 4ength 5aginal-probe sonographic cervical assessment has been evaluated e/tensively during the past t$o decades" 6hen performed by trained operators, cervical length analysis using transvaginal sonography is safe, highly reproducible, and more predictive than transabdominal sonographic screening (American College of 7bstetricians and 3ynecologists, &8'&b!" -nlike the transabdominal approach, transvaginal cervical sonography is not a9ected by maternal obesity, cervi/ position, or shado$ing from the fetal presenting part" #echni:ue is important, and ;ost and colleagues ('