Cosentyx (secukinumab) is a biologic drug that is used to treat several autoimmune diseases, including psoriasis, psoriatic arthritis, and ankylosing spondylitis. As per the provided sources, the effect of Cosentyx on fetal development is not entirely clear.

The FDA has classified Cosentyx as a pregnancy category B drug, which means that animal reproduction studies have not shown any adverse effects on the fetus, but there are no adequate and well-controlled studies in pregnant women [2]. Additionally, the FDA recommends that Cosentyx should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus [2].

A study published in the British Journal of Dermatology found that Cosentyx does not appear to increase the risk of adverse pregnancy outcomes, such as preterm birth, low birth weight, or congenital malformations [3]. However, the study was limited by its small sample size and the fact that it only included women with psoriasis [3].

In conclusion, the effect of Cosentyx on fetal development is not entirely clear, and there are no adequate and well-controlled studies in pregnant women. While animal studies have not shown any adverse effects on the fetus, the FDA recommends that Cosentyx should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Pregnant women should consult with their healthcare provider before using Cosentyx or any other medication [2].

Sources:
[2] https://www.accessdata.fda.gov/drugsatfda_docs/nda/2015/125504Orig1s000ODMemo.pdf
[3] https://onlinelibrary.wiley.com/doi/full/10.1111/bjd.16901