Gestational treatment

Tetrachlorodibenzo-p-dioxin elicited no apparent prenatal or postnatal effects when doses of up to 800 /xg/kg/day were given orally for 10 days of gestation. Treatment with 250-2000 /xg/kg/day of 2,7-di-chlorodibenzo-p-dioxin (99% purity) had no significant effect on prenatal and postnatal measures of toxicity but caused a low incidence of cardiac lesions. 2,3-Dichlorodibenzo-p-dioxin and 2-chlorodibenzo-p-dioxin up to 2000 /xg/kg/day had no adverse effect on survival, average weight, and skeleton of term fetuses. 

In the same study (Desi et al. 1998), no significant effects on these end points were seen in male rats exposed to methyl parathion only through the treatment of their dams during gestation or gestation and laetation these results are presented in Seetion 3.2.2.6. 

Oral treatment of pregnant dams with 0.25 /xg (or more) /kg/day of 2,3,7,8-tetrachlorodibenzo-p-dioxin for 10 days during gestation resulted in adverse effects on rat development. No adverse effects were seen at the 0.125 ju,g/kg/day. When C-2,3,7,8-tetrachlorodibenzo-p-dioxin (2.99 fjLc/mg) was given at 2 /xg/kg/day there was activity, primarily in liver and to a lesser extent, in fat and brain. When a single oral dose of 200 /Ag/kg was administered on gestation days 16, 17, or 18 and was followed 6 hours later with tissue sampling, the label was also observed in the fetus and placenta. Placenta had approximately twice as much label as the fetus. 

The incidence and severity of ROP both rise with decreasing birthweight and gestational age. Fielder et al. (1992) have shown that the incidence of ROP in infents of < 1700 g birthweight is about 50%, although only 5% had severe disease. Severe ROP results in vitreous haemorrhage from new vessel formation on the immature retina, retinal traction and eventually retinal detachment (Fig. 9.6). In the most severe cases, retinal detachment is complete, resulting in total blindness. Treatment with cryotherapy or laser has halved the incidence of retinal detachment. 

In rare instances (0.5% to 2% of pregnancies), NVP progresses to hyperemesis gravidarum.9 Treatment may require the use of enteral or parenteral nutrition if weight loss is present. A corticosteroid such as methylprednisolone may be considered. Methylprednisolone is associated with oral clefts in the fetus when used during the first trimester therefore, corticosteroids should be reserved as a last resort and should be avoided during the first 10 weeks of gestation.9,11... 

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