Abstract Background We present biochemical and clinical outcomes from 16 pregnancies in 7 patients with HypoPT. Case1 35y.o postsurgical HypoPT diagnosed(Dx) age27. Pregnancy1(P1): c-section(CS) at 34wks due to pre-eclampsia, BW 1995g with normal APGARS. Admitted for maternal hypercalcemia in 3rd trimester(T3). P2: abortion at 24wks (Trisomy21). P3: CS at 39wks, BW 2993g, calcium(Ca) requirements increased in T3 and decreased while breastfeeding(BF). Case2 39y.o postsurgical HypoPT Dx age34. P1: miscarriage at 8wks. P2: premature uterine contractions in T2 but was carried out to 40wks. Requirements decreased (Ca 44%,calcitriol 33%) due to hypercalcemia and hyperphosphatemia. P3: CS at 40wks. Both P2 and P3 complicated by neonatal hypercalcemia and hyperparathyroidism for 6mo. then recovered. Case3 32y.o postsurgical HypoPT, CS at 39wks, no neonatal complications, BW 3910g.Cae4: 32y.o postsurgical HypoPT Dx age24. P1: preterm at 33+4wks 2nd to PPROM, BW 2550g, normal APGARS. NICU x15 days for nutritional support. Maternal hypercalcemia in T2 (TUMS for GERD). Hypocalcemia and hypomagnesemia in T3 required IV replacement and doubling of Ca and calcitriol requirements. BF for 2mo., requirements decreased (Ca 60%,calcitriol 50%). P2: 28wks pregnant, requirements increased in T1 (Ca 18%,calcitriol 100%). Case5 30y.o GATA3 mutation confirmed age30 with bilateral deafness and CKD. P1: preterm at 36+5wks, BW 2850g. In T3, requirements decreased (Ca 25%, calcitriol 70%). Ca requirements unchanged while BF for 12mo. P2: miscarriage at 8wks. P3: CS at 35+6wks, pre-eclampsia, BW 3190g, APGARS 9/9 according to midwife, required NICU for respiratory distress at 10mins. Calcitriol decreased 66% at T2/T3 vs baseline. Postpartum hypocalcemia required 3X increase in Ca. Case6 31y.o idiopathic HypoPT Dx age22. P1: IVF required induction at 36wks for SGA, BW 1814g. Requirements increased during pregnancy (Ca 4%,calcitriol 150%) and decreased (Ca 10%,calcitriol 20%) while BF. P2: 6wks pregnant, Ca requirements unchanged. Case7 24y.o autosomal dominant hypocalcemia type1 (ADH1) Dx age 18mo. P1: induced at 37wks for "abnormal fetal doppler", BW 2825g, NICU x2wks for hypocalcemia 2nd to ADH1, normal APGARS. Ca and calcitriol requirements increased 3X in T2. Ca requirements declined to baseline, and calcitriol declined by 50% in T3. Required 3 admissions for hypocalcemia. P2: CS at 34wks for low BPP 2/8, APGARS 7/9, BW 2540g, required NICU for hypocalcemia. Required doubling of calcitriol in T1. Requirements increased in T2(Ca 50%,calcitriol 20%) and required 2 admissions for hypocalcemia. Requirements decreased during lactation (Ca 50%,calcitriol 60%). Conclusion Although our case series of pregnancy in HypoPT is relatively small, we document a high prevalence of neonatal and maternal morbidity despite close monitoring of serum calcium throughout pregnancy aiming for a normal serum corrected calcium. Poor compliance contributed to poor outcomes. Women with nonsurgical HypoPT had a higher rate of preterm delivery (4/5 deliveries) vs (2/5). Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.