Australian Birth Defects Society

A Society devoted to the study of birth defects


In an ideal world all pregnancies would be planned, however the reality is that around 50% of western pregnancies are unplanned. This can result in exposures occurring before a woman realises that she is pregnant, and often causes significant worry for both the pregnant woman and her health care providers. Frequently these exposures do not increase the risk of either miscarriage or birth defects compared with the general population, and evidence based counselling can reassure those women with wanted pregnancies that considering termination is unnecessary.

Previously here “In the clinic” we have looked at some exposures known to increase the chance of baby being born with a birth defect with exposure at a particular dose. Below are two common scenarios, where early exposure to an Australian Pregnancy Category D medication (drugs which have caused, are suspected to have caused or may be expected to cause an increased incidence of human foetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Accompanying texts should be consulted for further details). In the examples below, reassurance can be given to the pregnant woman based on the timing of the exposure.



Doxycycline and minocycline are antibiotics belonging to the tetracycline group. Tetracycline antibiotics are known to produce dental staining and reduction of long bone growth in a proportion of exposed foetuses. Doxycycline is prescribed to women in their childbearing years as a medicine for preventing malaria (when travelling to areas with chloroquine resistant malaria). Doxycycline and minocycline can also be used in the treatment of severe acne, and other infections where indicated as the most effective antibiotic.

When women become pregnant while taking tetracycline antibiotics, they may be advised to consider termination of pregnancy, on the basis of the drug being assigned Category D.

BUT…..tetracycline mediated potential adverse effects for baby are caused by the medication binding to calcium, and then being deposited in developing teeth and bones. The mineralisation of these structures is not occurring in the developing baby during the first trimester, so a woman who is exposed to these medicines early in pregnancy can be reassured that her baby has no increased chance of being born with a birth defect than the baseline population risk.



ACE inhibitors are a group of medications used to treat high blood pressure, including captopril, enalapril and ramipril. The ACE inhibitor group are all classified as Australian pregnancy category D. The ACE inhibitor medicines are known to affect an unborn baby’s renal function, with many potential harmful effects resulting from low urine output which can affect skull development and lung development, can produce growth restriction and limb contractures, and can even result in death of the baby.   

BUT…. These effects only occur when the pregnant woman takes the ACE inhibitor during the second and/or third trimester of pregnancy. Women exposed in early pregnancy may be reassured that use during the first trimester does not seem to present a significant risk to the foetus.                                         

For specific information regarding your particular medications in pregnancy or breastfeeding call MotherSafe 02 9382 6539 or 1800 647 848 (from country NSW only).

Page updated 11 August 2017

Previous ….

Mother Safe Logo

MotherSafe is a free telephone service for the women of NSW, based at the Royal Hospital for Women, Randwick.

Unplanned pregnancy Part two: an exposure has occurred before a woman realises she is pregnant, but does not increase risk over the baseline for her pregnancies, because the particular exposure is of concern in later pregnancy.