Most traditional nail polishes are rated between 5-7 on the EWG SkinDeep Database (Moderate - High hazard), but since nail polish is not applied to the skin, or purposefully ingested, the potentially harmful chemicals are not easily absorbed into the body. But if you are a nail biter - these chemicals should be of concern to you. Unfortunately, many nail polishes contain dibutyl phthalate and toluene which are both linked to reproductive toxicity and endocrine disruption. FDA research has also shown that methyl methacrylate and acetonitrile break down into cyanide when ingested.
Kim Kardashian (a role model for many young women around the world) recently posted pictures of herself biting her nails on Instagram. The star recently announced she is expecting a child with Kanye West.
If you don't bite or pick at your nails, and you paint them in a well vented area, its safe to have painted nails during pregnancy. Otherwise, try non-toxic nail polishes, like Knocked Up Nails which is specifically formulated to be safe for pregnant women.