I took NPH years ago, but I honestly can't remember what I was taking when I was pregnant (25 years ago). I do remember having issues with the "peak" effect of NPH because I've always worked full time and couldn't always control my schedule so that peak tended to catch me off guard with lows at inconvenient times. My life changed for the better once I was put on Lantus.
According to a chart I found, NPH is considered an intermediate acting insulin which starts 1-3 hours after injection, peaks at 4-9 hours and ends 14-20 hours with lows most likely between 4-16 hours.
I just found an article that stated Levemir was approved by the FDA for diabetes during pregnancy in the U.S. - the article was dated April 3, 2012. NPH was considered the gold standard of care during pregnancy up until this approval.
Also, this is from the Levemir website:
"Levemir® is also the first and only long-acting insulin analog that can be used during pregnancy without increasing the risk of harm to the unborn baby."
Best wishes SugarDragon and congrats on your pregnancy! :)