Drugs can have harmful effects on the fetus at any time during pregnancy. It is important to remember this when prescribing for a woman of childbearing age. However, irrational fear of using drugs during pregnancy can also result in harm. This includes untreated illness, impaired maternal compliance, suboptimal treatment and treatment failures. Major congenital malformations occur in 2–4% of all live births, 15% of all diagnosed pregnancies will result in fetal loss. During the first trimester, drugs may produce congenital malformations (teratogenesis), and the greater risk is from third to the eleventh week of pregnancy. During the second and third trimester, drugs may affect the growth and functional development of the fetus or have toxic effects on fetal tissues. Drugs given shortly before term or during labor may have adverse effects on labor or on the neonate after delivery. Few drugs have been shown conclusively to be teratogenic in man but no drug is safe beyond all doubts in early pregnancy. Screening procedures are available where there is a known risk of certain defects.Prescribing in Pregnancy
Since, approximately 50% of pregnancies are unplanned and rest 50% are planned, if possible, counseling of women before a planned pregnancy should be carried out including discussion of risks associated with specific therapeutic agents, traditional drugs (alternative medicines), over the counter drugs and substances of abuse such as opioids, smoking, alcohol, etc. Drugs should be prescribed in pregnancy only if the expected benefits to the mother are thought to be greater than the risk to the fetus. All drugs should be avoided if possible during the first trimester. Drugs which have been used extensively 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. Keeping in view the prevalence of irrational polypharmacy, emphasis should be laid on promoting the use of well-known single component drugs to multicomponent drugs. Since, there does appear to be an association of very potent topical corticosteroids with low birth weight, even the dermatological drug products being used should be cautiously selected and used.
The pronounced and progressive change in drug disposition that occurs during pregnancy is another major reason which calls for attention. Major physiological changes which influence drug disposition in mother and fetus are:
S.No. | Physiologic changes | Effects |
1. |
Plasma albumin concentration of mother reduced |
Drug protein binding alteration |
2. |
Increased body fat in mother |
Distribution of drug is effected |
3. |
Increased hepatic metabolism in mother |
Faster hepatic clearance |
4. |
Increased cardiac output in mother |
Increased renal blood flow and glomerular filtration and hence, increased elimination of drug |
5. |
Presence of placental barrier |
Selectivity of drug permeation based on its hydrophobicity or molecular weight of drug |
6. |
Drug metabolizing enzymes activity in fetal liver is very low |
Slow elimination of drugs by fetus |
Though maternal medication carry the risk of increase in the incidence of abortion, stillbirths, fetal death, premature or delayed labor or create perinatal problems; but certain medications like folic acid are recommended for all pregnant women to reduce the rate of congenital anomalies specifically, the neural tube defect.
The Food and Drug Administration has categorized the drug risks to the fetus that runs from: “Category A” (safest) to “Category X” (known danger--do not use!)
Controlled studies in women fail to demonstrate a risk to the fetus in the first trimester (and there is no evidence of a risk in later trimesters), and the possibility of fetal harm appears remote.