According to the Health Canada product monograph, you should consult a doctor prior to consuming any hydrolyzed collagen if you are pregnant or breastfeeding. If approved by your doctor, consuming hydrolyzed marine collagen can provide significant health benefits during pregnancy and post-partum. In fact, the amino acid glycine (found in marine collagen and collagen-rich foods) is of great importance during pregnancy, as it is needed for the synthesis of the placenta. The fetus also requires glycine, which it receives from the mother's blood via the placenta. For this reason, research has suggested that it is important for expectant mothers to obtain adequate amounts of glycine during pregnancy:
"Mother's best source of glycine is collagen-rich foods. Glycine balances methionine, an amino acid found in eggs and meat. When we consume large amounts of methionine from muscle meats, we need glycine to safely dispose of it; otherwise it can disrupt cellular communication. Folate from liver, legumes and green vegetables work together with glycine to help the body clear methionine. It is important, therefore, for the expectant mother to liberally match her muscle meat consumption with glycine-rich foods" (Dr. Cowan, S. Fallon Morell, 2013, p. 25-26).
Many women find there to be no concerns with postpartum consumption of hydrolyzed marine collagen and experience its many benefits, including improved hydration, firmness and elasticity of skin and thicker hair and nails.
References:
Dr. T, Cowan, Fallon Morell, S (2013). The Nourishing Traditions Book of Baby & Child Care.