mechanisms behind adverse pregnancy outcomes with PFOS exposure remain unclear. One proposed cause has to do with PFOS impairment on placental blood flow. This mechanism could help explain several of the pregnancy-related outcomes from PFOS exposure including such as intrauterine growth development, low birth weight, preterm birth labor, and preeclampsia. Additional physiological mechanisms may include disruption in inflammatory signals during pregnancy, decreased trophoblast signaling and trophoblast migration. Additionally, PFOS exposure has been shown to be related to the downregulation genes corresponding to growth factors, pregnancy-related signal transducers, and maternal hormones. PFOS impact on thyroid hormone regulation also has the potential to impact several birth outcomes. Breastfeeding and lactation PFOS has been measured in breastmilk and is estimated to contribute the greatest level of PFOS exposure in infants. Specifically, the duration of breastfeeding has been shown to be associated with increases in PFOS in infants. Some evidence has shown that breastmilk provides more than 94% of the PFOS exposure in infants up to six months old. The Agency for Toxic Substances and Disease Registry (ATSDR) concluded that breastfeeding benefits continue to outweigh potential risks associated with PFOS in breastmilk. Infertility PFAS compounds such as PFOS act as an endocrine disruptor of the reproductive system. As such, there is concern over the impact of this compound on fertility. There is some evidence to suggest that PFOS may impair fertility in both females and males. One study found that women with higher levels of PFOS and PFOA took longer to become pregnant than those with lower levels, suggesting that the chemicals may impair fertility. The impact of PFOS on male fertility is still under investigation. There have been some studies that demonstrated that PFOS is associated with a decrease in sperm count and as well as a decrease in the number of morphologically normal sperm. There has also been evidence to suggest that PFOS may also reduce testosterone levels. Thyroid disease Increased levels of PFOS have been shown to accumulate in thyroid gland cells and have been associated with altered thyroid hormone levels in adults. Appropriate levels of thyroid hormone during pregnancy are critical for a developing fetus as this hormone is involved with brain development and body growth. Studies have demonstrated a relationship between PFOS exposure and thyroid dysfunction during pregnancy resulting in altered thyroid hormone levels in both the mother and the fetus. Hypercholesterolemia PFOS has been associated with increased risk