Introduction

An abnormal fetal phenotype can be caused by environmental factors, chromosomal anomalies, specific genes, or more complex genetic mechanisms. Because families with single-gene (Mendelian) disorders or parental chromosomal anomalies have the greatest chance of having children with genetic conditions, it is important to identify couples from such families before they undertake pregnancy

An assessment of a couple's risk can often be made by a combination of:

Particular pointers that might suggest that a couple is at increased risk of having a child with congenital anomalies include:

• A previous child affected with a single-gene disorder• A family history of a single-gene disorder• A parent with a chromosomal anomaly• Parental consanguinity• Advanced maternal age• Maternal illness or medication; maternal exposure to teratogens• Result of first- or second-trimester combined Screening

Determining the Genetic Basis of a Condition

To ensure that a family receives accurate genetic information, it is recommended that the following steps are undertaken:

Identifying Families with an Increased Probability of a Genetic Condition

The couple may have realized that the family tree suggests a genetic condition and volunteer this information. In other cases, a high risk is appreciated only when a formal history is taken.