Protein S deficiency represents a rare but significant hereditary thrombophilia that poses substantial risks during pregnancy, yet clinical management remains controversial due to limited evidence-based guidance. A retrospective case-control study investigated the effects of low molecular weight heparin (LMWH) prophylaxis on pregnancy outcomes in women with suspected protein S deficiency, providing crucial insights into optimal anticoagulation strategies for this high-risk population. Conducted at Peking University People's Hospital between November 2012 and May 2024, the study analyzed 35 pregnant women with protein S activity levels indicating suspected deficiency, comparing 20 women who received LMWH prophylaxis with 15 who received standard care without anticoagulation, alongside 70 healthy pregnant controls.
The pathophysiological rationale for this investigation stems from the hypercoagulable state of pregnancy, which increases venous thromboembolism risk 15-35 fold compared to non-pregnant women, with particularly elevated risk in the postpartum period. Protein S deficiency exacerbates this vulnerability by impairing inactivation of procoagulant factors Va and VIIIa, thereby increasing thrombin generation. Furthermore, protein S deficiency has been associated with adverse pregnancy outcomes including recurrent pregnancy loss, preterm labor, and fetal growth restriction, potentially through placental microvascular thrombosis and impaired trophoblast differentiation. Despite these established risks, international guidelines lack consensus on thromboprophylaxis for protein S deficiency during pregnancy, with recommendations varying from routine antepartum and postpartum prophylaxis to surveillance-only approaches depending on family history and additional risk factors.
The study employed specific diagnostic criteria for suspected protein S deficiency: protein S activity below 55% in the non-pregnant state, below 30% in the second trimester, or below 24% in the third trimester. These thresholds account for the physiological decrease in protein S levels during normal pregnancy. Notably, the majority of participants did not undergo PROS1 genetic testing, which represents the diagnostic gold standard, due to cost considerations and clinical practice patterns. However, the study design reflects real-world clinical scenarios where protein S activity measurement guides management decisions.
Baseline characteristics revealed significant differences between groups. Women with protein S deficiency demonstrated substantially higher rates of in vitro fertilization-embryo transfer conception compared to controls (28.6% versus 5.7%), suggesting an association between protein S deficiency and reduced natural fecundity. History of recurrent pregnancy loss was significantly more prevalent in the protein S deficiency group (34.3% versus 5.7%), underscoring the clinical importance of this condition. The LMWH-treated group had higher maternal age and greater utilization of aspirin combination therapy compared to the untreated group, reflecting clinician preference for more aggressive management in perceived higher-risk patients.
The primary outcome analysis demonstrated dramatic differences in live birth rates between treatment groups. All 20 women receiving LMWH prophylaxis achieved live births, compared to only 8 of 15 women (53.3%) in the untreated group. This difference achieved statistical significance despite the limited sample size. Multivariable logistic regression adjusting for maternal age, VTE risk score, IVF conception, and aspirin use yielded an adjusted odds ratio of 31.10 for live birth with LMWH treatment, though with wide confidence intervals reflecting the small sample size. Age-stratified analysis revealed particularly pronounced benefits in women over 32 years, where LMWH achieved 100% live birth rates versus 33.3% in untreated patients, suggesting enhanced therapeutic utility in older gravidae with protein S deficiency.
Secondary outcomes including venous thromboembolism, preeclampsia, and fetal growth restriction occurred too infrequently to permit meaningful statistical comparison. Notably, no hemorrhagic complications or heparin-induced thrombocytopenia occurred in the LMWH-treated group, supporting the safety profile of prophylactic anticoagulation in this population. Neonatal outcomes including birth weight, Apgar scores, and congenital anomalies showed no significant differences between groups.
The study's findings align with prior meta-analyses suggesting LMWH may reduce adverse pregnancy outcomes and improve live birth rates in women with hereditary thrombophilia. However, the authors appropriately acknowledge significant limitations including the retrospective design, small sample size, single-center setting, lack of genetic confirmation for most participants, and potential confounding by indication given that clinicians selected patients for LMWH treatment based on perceived risk. The 100% live birth rate in the LMWH group, while encouraging, may reflect selection bias toward lower-risk patients or chance given the small numbers.
From a clinical practice perspective, these results support consideration of LMWH prophylaxis for pregnant women with significant protein S deficiency, particularly those with additional risk factors such as advanced maternal age or prior adverse pregnancy outcomes. The safety profile appears favorable, with no increase in bleeding complications observed. However, the optimal timing of LMWH initiation remains uncertain, as women starting prophylaxis across all trimesters achieved successful outcomes, though earlier initiation may provide additional benefits in preventing early pregnancy loss that could not be evaluated in this study.
Future research directions highlighted include prospective randomized trials with adequate power to definitively establish LMWH efficacy, investigation of optimal prophylaxis timing, and evaluation of whether combination therapy with aspirin provides incremental benefit over LMWH monotherapy. Multi-center studies involving diverse populations are needed to validate these preliminary findings and establish evidence-based management guidelines for this challenging clinical scenario.
In conclusion, this study provides preliminary evidence that LMWH prophylaxis may significantly improve live birth rates in pregnant women with suspected protein S deficiency, particularly among older patients. While limited by methodological constraints, the findings contribute to the evidence base for managing this rare but high-risk thrombophilia during pregnancy and support a proactive approach to anticoagulation in affected women.
DOI
10.1007/s11684-025-1189-4