Effects of metals on female reproduction may arise from their action on several stages beginning in fetal life, during early development or maturity, and include manifestations such as subfertility, infertility, intrau-terine growth retardation, spontaneous abortions, malformations, birth defects, postnatal death, learning and behavior deficits, and premature aging. Because it is difficult to obtain detailed information concerning effects on the reproductive system in humans, evidence is usually limited to animal data or studies on fertility and spontaneous abortions. Pregnancy loss is the endpoint most frequently used to monitor effects on female reproductive function, starting from early losses, which contain a large proportion of chromosomal abnormalities and may represent 35-40% of human pregnancies. The remaining 10-15% later abortions are clinically manifest, and some have been linked to environmental factors (Miller et al, 1980; Runnebaum et al., 1997). Thus, there seems to be a remarkably high background rate of fetal loss in humans.
The clinical and epidemiological findings related to metal-induced effects on female reproduction are often difficult to interpret, because many other factors may influence the outcome such as age, ovarian reserve, hormonal imbalance, behavior, genetics, male fertility factors, or sexually transmitted diseases. In addition, timing, duration, and intensity of exposure are important in assessing reproductive adverse effects. Ernhart (1992) pointed out some critical aspects in measuring the dose indicators, such as sampling time and the matrix (maternal or fetal blood, cord blood, or placenta) in which indicators of prenatal exposure should be determined. To better assess early exposure to metals and the trend of absorption through pregnancy, at least one sample should be taken during the first trimester and another during the last 6 weeks of the pregnancy. This will facilitate the assessment of effects on the various stages of development and organogenesis.
Knowledge about pathogenetic mechanisms of female reproductive damage is limited. Effects may be direct, when environmental or occupational metals interact with specific reproductive target organs, or indirect, when metals act on endocrine or other systems. The ovaries and ova are susceptible to direct damage by metals for an extended period of time, from meiosis through ovulation. Some experimental studies suggest an increased risk of miscarriage, fetal malformation, placental insufficiency, and premature birth because of metal exposure (Fagher et al., 1993; Laundanski et al., 1991). Metals such as lead may interfere with the hypothalamic-pituitary-ovarian axis at different levels by modifying the secretion of prolactin, adrenocorti-cal steroids, or thyroid hormones; vascular effects on the placenta have also been suggested (Gerhard et al., 1998; Hertz-Picciotto and Croft, 1993; Piasek and Laskey, 1994).
Current evidence provides warning signals: the female reproductive system is vulnerable to toxic agents, and the number of working women potentially exposed to metals is increasing worldwide. It is estimated that most of working women are in reproductive age; about half of working women are used during pregnancy, and about 20% are exposed to chemicals of potential concern (Sharara et al., 1998). Reviews on female reproductive effects include Gold and Tomich (1994), Gardella and Hill (2000), Foster (2003), and Kumar (2004).
Was this article helpful?
Prior to planning pregnancy, you should learn more about the things involved in getting pregnant. It involves carrying a baby inside you for nine months, caring for a child for a number of years, and many more. Consider these things, so that you can properly assess if you are ready for pregnancy. Get all these very important tips about pregnancy that you need to know.