16.
Reproductive Problems
Authors
The information in this chapter was prepared by Tim Flood, M.D., Medical Director, Chronic Disease Epidemiology Section, Arizona Department of Health.
Introduction
This analysis differs from the others in this section in that it addresses a group of health outcomes, rather than a specific environmental cause. As will be clear, we know very little about the environmental causes of most reproductive problems.
There are a number of things that can go wrong in the area of reproductive health.
o Infertility can affect the male or female. Very rarely have scientists been able to link infertility to environmental factors.
In one notorious example at a pesticide manufacturing plant, DBCP was shown to be the cause of decreased sperm count and failure to father offspring. However, at this time, it is not possible to generalize this single example, nor about the number of instances in which environmental exposures are causing infertility.
o Adverse reproductive outcomes. The background frequency of this problem is shown in Table 16.1 on the next page.
Table 16.1 Frequency of Selected Adverse Pregnancy Outcomes in Humans
----------------------------------------------------------------------------------- | Event | Frequency | Unit | | | per 100 | | =================================================================================== | Spontaneous abortion, 8-28 weeks | 10-20 | Pregnancies or women | ----------------------------------------------------------------------------------- | Chromosomal anomalies in | 30-40 | Spontaneous abortions | | spontaneous abortions, 8-28 weeks | | | ----------------------------------------------------------------------------------- | Chromosomal anomalies in | 2 | Amniocentesis specimens | | amniocentesis | | | ----------------------------------------------------------------------------------- | Stillbirths | 2-4 | Stillbirths and live births | ----------------------------------------------------------------------------------- | Low birthweight (less than 2500g) | 7 | Livebirths | ----------------------------------------------------------------------------------- | Major malformations | 2-3 | Livebirths | ----------------------------------------------------------------------------------- | Chromosomal anomalies | 0.2 | Livebirths | ----------------------------------------------------------------------------------- | Severe mental retardation | 0.4 | Children to 15 years of age | -----------------------------------------------------------------------------------
Birth Defects
Birth defects are recognized in about 2.8% of Arizona's infants up to age one year (ADHS, 1993). Scientists estimate that up to 16% of persons of all ages have birth defects that appear at some time during a lifetime. What causes these defects? According to Manson and Wise:
-------------------------------------------------------------- | Most studies of the effects of chemicals on reproductive | | health are conducted in the occupational setting because | | it is sometimes possible to categorize the workers' | | exposures and to assess the outcome, for example a child | | with a birth defect. Such studies occasionally show an | | elevated risk for working in a particular job like | | painting, or for exposure to a class of chemicals like | | solvents. | --------------------------------------------------------------
However, few of these studies have been replicated. Replication is important for confirming the findings of previous studies and convincing experts that an environmental exposure causes an adverse effect. The net result is that there are few known exposures to environmental chemicals that experts say can cause birth defects.
Solvents
Slight progress has been made in the investigation of solvents.
The specific solvent(s) responsible for the increased risk is not known.
Many consumers are unaware of the exposure and potential hazards associated with household products and the activities of daily living. Prudence would suggest that persons planning a pregnancy should minimize their exposure to a number of products.
Causes of Birth Defects
The best estimate of teratologists is presented in Table 16.2. The Committee has modified the table for ACERP and estimated the approximate number of cases that might be occurring if the same rates apply to Arizona.
Table 16.2 Attributed Causes of Congenital Anomalies
---------------------------------------------------------------------------------------- | Cause | Percent | Estimated | | | | Arizona Cases | | | | In 1992 | ======================================================================================== | Monogenetic causes (single mutant gene: recessive and | 7.5 | 145 | | dominant; autosomal and gonosomal) | | | ---------------------------------------------------------------------------------------- | Chromosomal causes | 6.0 | 116 | ---------------------------------------------------------------------------------------- | Environmental causes: | 2.0 | 39 | ---------------------------------------------------------------------------------------- | All maternal infections (rubella, toxoplasma, | 1.5 | 29 | | CMV; herpes, other viruses and organisms) | | | ---------------------------------------------------------------------------------------- | Diabetes (1.4%); other maternal illnesses | 1.5 | 29 | | (PKU, tumors, dysthyroidisms (<<1%)) | | | ---------------------------------------------------------------------------------------- | Anticonvulsant drugs and other environmental | 20 | 386 | | substances and chemicals | | | ---------------------------------------------------------------------------------------- | Eco-genetic interactions | 60 | 1,159 | ---------------------------------------------------------------------------------------- | Unknown | 100.0 | 1,932 | ----------------------------------------------------------------------------------------
Scientists believe that most birth defects arise through the effect of a teratogen on the developing organs of the embryo during a highly sensitive period. This occurs during the third to the eighth week of the pregnancy, when development of most organs occurs. This occurs so early that most women would not recognize that they are indeed pregnant. It is during this period that exposure to environmental agents should be avoided.
The reader should not be left with the impression that all the news about reproduction and the environment is bad. Recent studies show that daily intake of about 0.4 micrograms of the vitamin folic acid can reduce the risk for neural tube defects such as spina bifida and anencephaly.
Current public health efforts are underway to encourage women considering pregnancy to eat a balanced diet that contains folic acid and to take a prenatal vitamin with folic acid. The challenge is to ensure that women are consuming the proper diet at the time of conception, and that there is sufficient intake of the vitamin to carry her through the period of morning sickness.
Conclusion
One reason why the causes of reproductive problems is mostly unknown is because this topic has received comparatively little research support. Studies that search for teratogens are difficult to conduct, labor intensive, and subject to methodological biases.
While procreation is a very sensitive and private aspect of a couple's relationship, there is potential for conducting meaningful studies in the area of reproductive health. For example:
o The most vulnerable period (around the first trimester of pregnancy) is comparatively short. This situation is different than for a disease such as cancer which takes years to develop and is therefore more difficult to study.
o Many adverse reproductive outcomes are readily apparent at birth, a distinct advantage in identifying the outcome to be studied.
o Most women are willing to participate in studies that document their environmental exposures during pregnancy.
All of these reasons favor studies of reproductive problems.
The issues of reproductive health were of great concern to the Committee. However, based on the scarcity of identifiable risk factors, the Committee was unable to rank this issue. It remains an area for future research.