Calcium homeostasis in pregnancy during long-term heparin treatment

Short-term low-dose heparin plus bedrest impairs bone metabolism in pregnant women

OBJECTIVE

To assess the osteoporotic risk of short-term low-dose heparin plus bedrest in pregnancy.

STUDY DESIGN

In a prospective case-control study, 10 pregnant women on bedrest receiving prophylactic unfractionated heparin 10,000 IU per day for 7-46 days pre-study and 28 days per-study were compared with 6 normal pregnant controls of similar maternal and gestational age and 10 nonpregnant women of similar age. Serum ionised calcium, 1,25-dihydroxyvitamin D(3), osteocalcin, and urinary calcium/creatinine ratio were determined three times at 2-week intervals.

RESULTS

1,25-Dihydroxyvitamin D(3) was lower in the treated group than in pregnant controls throughout (P<0.03). Osteocalcin was lower at study start than end in both pregnant groups (P<0.05), and lower in the treated group than in either pregnant (n.s.) or nonpregnant controls (P<0.005). Calcium/creatinine ratio differences were non significant (n.s.).

CONCLUSION

Short-term low-dose heparin plus bedrest suppresses 1,25-dihydroxyvitamin D(3) and osteocalcin levels in pregnancy.

Parathyroid disorders of pregnancy

Diseases of the parathyroid gland are uncommon in women of childbearing age. However, total serum calcium is lower in normal pregnancy, but ionized serum calcium remains within normal limits. Serum parathyroid levels are slightly decreased in the second half of pregnancy. Primary hyperparathyroidism, if unrecognized, may increase maternal and fetal morbidity, which is related to the level of serum calcium. The most common cause is a single parathyroid adenoma, accounting for about 80% of cases. Maternal complications include acute pancreatitis, hypercalcemia crisis, and toxemia. An increased incidence of prematurity and neonatal hypocalcemia has been reported when maternal hypercalcemia is significantly elevated. Other causes of hypercalcemia are rare in pregnancy. Hypoparathyroidism is seldom seen in pregnancy; the most common cause is after surgical throidectomy. The doses of vitamin D and calcium do not change during pregnancy; however, hypercalcemia may develop in the postpartum period. Serum calcium should be determined at every trimester of pregnancy and at regular intervals after delivery, and in a significant number of patients, the dose of vitamin D should be reduced. Osteoporosis has been recognized most frequently in the last few years. It appears that those patients with a family history of osteoporosis and those on heparin therapy have a tendency to develop symptoms of the disease in pregnancy. Finally, lactation is not contraindicated in women with osteoporosis; although there is a slight decrease in bone density in the few months after delivery, this is a transient event and bone densitometry returns to prepregnancy levels in most women. Recent studies indicate that there is no need for calcium therapy during lactation with few exceptions, such as lactating adolescents, mothers nursing more than one child, and mothers with closely-spaced pregnancies.

Hazards of heparin: allergy, heparin-induced thrombocytopenia and osteoporosis

Heparin is the commonest mode of thromboprophylaxis used in pregnancy. It does not cross the placenta but has potential adverse effects on the mother, of which the most important is heparin-induced osteoporosis. The hazards of heparin, including bleeding, skin reactions, heparin-induced thrombocytopenia and osteoporosis are discussed and the relevant literature reviewed. Low-molecular-weight heparins have certain advantages over standard unfractionated heparins, especially in obstetrics. Their longer half-life and increased bioavailability enable once-daily injections, making them more convenient and acceptable. They are as effective as standard heparin but have a theoretically more favourable side-effect profile, providing less anticoagulant relative to antithrombotic activity. Current evidence suggests a lower incidence of heparin-induced thrombocytopenia. A reduced risk of osteoporosis is suggested but not yet proven. Although thrombo-embolism is currently the leading cause of maternal mortality in the UK, antenatal heparin prophylaxis is not given to all women with previous thrombo-embolism because of continued fears concerning heparin-induced osteoporosis. A protocol is presented with guidelines for different levels of obstetric prophylaxis depending on the perceived level of risk.

Bone density studies in pregnant women receiving heparin

Lumbar spine bone density falls during pregnancy in both women who are treated with heparin and those who are not. Breast feeding delays recovery to baseline values until suckling stops.

A prospective study of heparin-induced osteoporosis in pregnancy using bone densitometry

OBJECTIVE

Our purpose was to evaluate the subclinical occurrence of heparin-induced osteoporosis in pregnancy, by means of bone densitometry.

STUDY DESIGN

A prospective, consecutive cohort of 14 pregnant women requiring heparin therapy and 14 pregnant controls matched for age, race, and smoking status was identified by 20 weeks' gestation at a university medical center. Proximal femur bone density measurements were taken at baseline, immediately post partum, and 6 months post partum in the cases and controls. Vertebral measurements were also obtained on both groups immediately post partum and 6 months post partum. Bone density as a function of heparin dosing and duration was examined. Nonparametric statistical tests were used for all comparisons.

RESULTS

Five of 14 cases (36%) had a > or = 10% decrease from the baseline proximal femur measurements to immediate postpartum values versus none of the 14 matched controls (p = 0.04). Mean proximal femur bone density measurements also decreased in the cases (p = 0.01); this difference continued to be statistically significant 6 months post partum (p = 0.03). No dose-response relationship could be demonstrated.

CONCLUSION

Heparin adversely affected bone density in about one third of exposed patients.

Osteoporotic fractures and the recurrence of thromboembolism during pregnancy and the puerperium in 184 women undergoing thromboprophylaxis with heparin

OBJECTIVE

To study the effect of long-term treatment during gestation with heparin on the incidence of osteoporotic fractures and thromboembolic recurrence.

STUDY DESIGN

Long-term subcutaneous prophylaxis with heparin twice daily in pregnancy was prescribed for 184 women, during a decade because of an increased risk of thromboembolism. The dosage of heparin was adjusted to anti-factor Xa activity or activated partial thromboplastin time and different regimens were given, depending on the risk of recurrence.

RESULTS

For the total group the mean dosage of heparin ranged from 13,000 to 40,000 IU per 24 hours (mean 19,100 IU per 24 hours), and the average duration of treatment was 25 weeks. Symptomatic osteoporotic fractures of the spine occurred post partum in four women, for whom the mean dosage of heparin ranged from 15,000 to 30,000 IU per 24 hours (mean 24,500 IU per 24 hours), and the duration of treatment ranged from 7 to 27 weeks (mean 17 weeks). In spite of prophylaxis with heparin, thromboembolic complications occurred in five women. They had either nonsatisfactory concentrations of heparin according to our regimen or were later diagnosed as having a coagulation disorder known to increase the risk of thromboembolism.

CONCLUSION

Osteoporotic vertebral fractures were found in 2.2% of the women, and a relationship to the amount of heparin was indicated, although fractures were not avoided during low-dose, short-term prophylaxis. Recurrence of thromboembolism occurred in 2.7% of the patients, but if a strict heparin adjustment had been performed, recurrence could probably have been prevented.