Determining Pregnancy Cohort
IBM® MarketScan® Commercial Database that includes health insurance
claims data from across the US from 2007 to 2016 were used. A cohort of
women aged 12–55 years with singleton pregnancies was identified from
the IBM MarketScan Commercial Database inpatient admissions by using
International Classification of Diseases, 9th Revision, Clinical
Modification (ICD-9) diagnosis codes (640-649 (Complications mainly
related to pregnancy), 650, 652-659 (Normal delivery, and other
indications for care in pregnancy, labor, and delivery), 660-669
(Complications occurring mainly in the course of labor and delivery),
670-677 (Complications of the puerperium), 678-679 (Other maternal and
fetal complications), V27.0, V27.1, V27.9 (Outcome of delivery); only
codes ending in ***.*1 and ***.*2 identifying delivery were used),
ICD-10 codes (O80-O83 (Single delivery), Z37.0, Z37.1, Z37.9 (Outcome of
delivery), O60.1*X0, O60.1*X1 (Preterm labor with preterm delivery),
O42.1 except O42.111, O42.1 except O42.111, O42.9 except O42.911
(Premature rupture of membranes)(Marić et al. 2019)), diagnosis-group
related (DRG) codes (765-766 (Cesarean section with/without complication
or comorbidity), 767 (Vaginal delivery with sterilization and/or D&C),
768 (Vaginal delivery with O.R. procedure except sterilization and/or
D&C), 774-775 (vaginal delivery with/without complications)) and
procedure codes (72.** (Forceps, vacuum, and breech delivery), 73.22,
73.59, 73.6 (Other procedures inducing or assisting delivery),
74.0-74.2, 74.4, 74.99 (Cesarean section and removal of fetus)) as
previously described in Marić et. al.8 Given the
differences in sPTB risk between singleton and multiple gestations,
deliveries with codes for multi-fetal pregnancies (ICD-9 codes 651,
V27.2-V27.7, V-91; ICD-10 codes O30) were excluded. To avoid
dependencies for women with multiple pregnancies, only the first
pregnancy recorded in the IBM MarketScan Commercial Database was
included. We excluded molar and ectopic pregnancies (ICD-9 codes 630 and
633; ICD-10 codes O00 and O01; DRG code 777), spontaneous and induced
abortions (ICD-9 codes 632, 634-637; ICD-10 codes O03), complications
following abortion, ectopic or molar pregnancies (ICD-9 code 639; ICD-10
codes O04 and O08), and abortions with/without D&C (DRG codes 770 and
779).
Gestational age (GA) at delivery was estimated by using the algorithm
described in Marić et. al.8 Briefly, the algorithm is
based on codes for the number of completed weeks of gestation (ICD-9
codes 765.2, 766.21, 766.22; ICD-10 codes Z3A) and codes for preterm
labor with preterm delivery (ICD- 9644.21; ICD-10 codes O60.1*X0),
identified directly from women’s records when present or, otherwise,
from infants’ records. To obtain GAs from infant records, single
liveborn infants were identified (ICD-9 codes V30 and V39; ICD-10 codes
Z38.0-Z38.2) and linked to their mothers. Women without a GA code either
in their own or their infant record, were assigned a GA of: 1) 34 weeks
if they were identified to have sPTB, as described below, or 2) 39
weeks, otherwise.