Pregnancy is a major event in any women’s life and is associated with physiological changes affecting especially the endocrine, cardiovascular and haematological changes.
Foetal development during the first 3 months of pregnancy is a complex process of organogenesis and the foetus is then especially at risk from developmental defects. The most critical period is the 3rd to 8th week, during differentiation. Most developmental defects are unknown aetiology but,in addition to hereditary influences, infections, alcohol, smoking and drugs can be implicated in some cases.
Drugs can have harmful effects on the embryo or fetus at any time during pregnancy. It is important to bear this in mind when prescribing for a woman of childbearing age or for men trying to father a child.
During the first trimester drugs can produce congenital malformations (teratogenesis), and the period of greatest risk is from the 3rd to the 11th week of pregnancy.
During the second and third trimesters drugs can affect the growth and functional development of the fetus or have toxic effects on fetal tissues. Drugs given shortly before term or during labour can have adverse effects on labour or on the neonate after delivery.
Drugs should be prescribed in pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus, and all drugs should be avoided if possible during the first trimester. Drugs which have been extensively used in pregnancy and appear to be usually safe should be prescribed in preference to new or untried drugs; and the smallest effective dose should be used.
Few drugs have been shown conclusively to be teratogenic in man, but no drug is safe beyond all doubt in early pregnancy. Screening procedures are available when there is a known risk of certain defects.
Absence of a drug from the list does not imply safety.
Drugs to avoid in pregnant mothers.
- Nitrous oxide-congenital anomalies
- Persistent pulmonary hypertension, bleeding tendency, premature closure of ductus arteriosus
- Aspirin – possible abortion, premature closure of ductus arteriosus, persistent pulmonary hypertension, bleeding tendency.
- Pentazocaine-foetal addiction and withdrawal syndromes
- Codeine – respiratory depression
- Cocaine- anlkyloglossia, risk of spontainious abortion,neonatal cerebral infraction,abruption placentae
- Tetracyclines – discoloured teeth and bone, altered bone growth
- Co-trimoxazole (trimethoprim+sulfamethoxazole)-haemolysis,teratogenicity,methamoglobinaemia
- Metronidazole-May be mutagenic?
- Acyclovir –teratogenicity
- Flucanazole-congenital anomalies
- Carbamazapine – neural tube defects,vitamin K impairment and bleeding tendency
- Valpolate-neural tube defects
- Phenytoin-fetal phenytoin syndrome
- Diazepam-cleft lip /palate
- · Avoid regular use (risk of neonatal withdrawal symptoms); use only if clear indication such as seizure control (high doses during late pregnancy or labour may cause neonatal hypothermia, hypotonia and respiratory depression)
- Carbimazole – Goitre
- Thalidomide-phocomalia(upper parts of limbs are not developed)
- Corticosteroids – adrenal suppression,growth retardation
· 1st trimester-hypoplastic nasal bridge
· 2nd trimester-CNS malformations
· 3rd trimester-risk of bleeding