Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

People considering fertility treatments should be aware that such treatments raise the risk of multiple births and that multifetal pregnancies are associated with an increased risk of some birth defects. The Table shows the results of Yiwei Tang’s study of birth defects reported in Florida from 1996 to 2000. Tang compared the incidence of various defects among single and multiple births. She calculated the relative risk for each type of defect based on type of birth, and corrected for other differences that might increase risk: maternal age, income, race, previous adverse pregnancy experience, education, Medicaid participation during pregnancy, and the infant’s sex and number of siblings. A relative risk of less than 1 means a defect occurs less often with multiple births than single births. A relative risk of greater than 1 means that multiples are more likely to have a defect.

Prevalence, per 10,000 Live Births, of Various Types of Birth Defects among Multiple and Single Births

Prevalence of Defect Relative Risk
Multiples Singles
Total birth defects 358.50 250.54 1.46
Central nervous system defects 40.75 18.89 2.23
Chromosomal defects 15.15 14.20 0.93
Gastrointestinal defects 28.13 23.44 1.37
Genital/urinary defects 72.85 58.16 1.31
Heart defects 189.71 113.89 1.65
Musculoskeletal defects 20.92 25.87 0.92
Fetal alcohol syndrome 4.33 3.63 1.03
Oral defects 19.84 15.48 1.29

Does a multiple pregnancy increase the relative risk of chromosomal defects in offspring?

Source: Y. Tang et al. 2006. The risk of birth defects in multiple births: A population-based study. Maternal and Child Health Journal 10:75–81.

Summary Introduction

To review:

Whether multiple pregnancies increase the relative risk of chromosomal defects in offspring.


A study was conducted in Florida during the time span of 1996–2000 on the newborns. This study was conducted on the prevalence of birth defects among the newborns per 10,000 live births. The study also included the prevalence of the defects among multiple and single births. The relative risk was also calculated for each defect. Birth defects are functional or structural abnormalities that are present in a newborn. These may develop either before or at the time of birth.


The calculation of relative risk for each defect can help in understanding its prevalence in either the single-birth group or the multiple-birth group. If the value of relative risk is lower than 1, it suggests that it occurs more in the single-birth group. If the value is higher than 1, it suggests that the defect occur more often in the multiple-birth defects.

According to the given data, the value of relative risk is higher than one for a total of 6 birth-defects. These are CNS defects, gastrointestinal defects, genital/urinary defects, fetal alcohol syndrome, and oral defects...

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