We tested whether direction-specific nocturnal cardiorespiratory coupling (CRC) in the first trimester differed in pregnancies that later developed obstetric complications. The analysis included 2504 nulliparous women from the nuMoM2b cohort with valid level 3 home sleep recordings at 6-13 weeks' gestation. Bidirectional CRC between RR intervals and abdominal respiratory effort was quantified using bivariate phase-rectified signal averaging in consecutive 5-min segments. Coupling strength, local transition dynamics, and waveform irregularity were summarized by nightly mean and standard deviation. Associations with gestational diabetes mellitus (GDM; n = 111), preeclampsia (n = 149), preterm birth (n = 192), and fetal macrosomia (n = 186) were examined using proportional-odds models with CRC feature quintile as the ordered outcome. Models included all four complications simultaneously and adjusted for maternal age, pre-pregnancy body mass index, race and ethnicity, gestational age at recording, relevant medical and family history, medication use, and apnea-hypopnea index >5 events/h. Holm correction was applied across outcomes. GDM was associated with lower respiration-to-heart rate coupling strength (cumulative odds ratio, 0.45; 95% CI, 0.31-0.64; P < 0.001) and shallower slope at the anchor point (0.63; 0.45-0.89; P = 0.03). Fetal macrosomia was associated with lower within-night variability in heart rate-to-respiration waveform irregularity (0.59; 0.45-0.77; P < 0.001). No associations with preeclampsia or preterm birth remained significant after correction. Direction-specific differences in nocturnal CRC were detectable in the first trimester in pregnancies that later developed GDM or resulted in fetal macrosomia.