French academics in an IVF clinic took regular pictures of an egg from the moment it was fertilized until it was ready to be implanted into the mother.
At all stages of development, embryos from smokers were consistently a couple of hours behind, a study showed, according to BBC News Thursday.
Researchers watched 868 embryos develop -- 139 from smokers. Scientists watched in real time how embryos develop without disturbing them.
In the clinic, the embryos of non-smokers reached the five-cell stage after 49 hours, BBC reported. In the smokers, it took 50 hours. The eight-cell stage took 62 hours in smokers' embryos, while non-smokers' embryos reached that point after 58 hours.
Senior embryologist and lead researcher, Dr. Thomas Freour, told the BBC: "Embryos from smoking women, they behave slower, there is a delay in their development.
"On average it is about two hours, it is significant and nobody knew that before."
This study cannot say what impact the slower development has, or if this affected the chances of having a child, the report said.
Dr. Freour speculated that "if they go slower, maybe something is starting to go wrong and they wouldn't implant," according to BBC.
The findings were presented at the European Society for Human Reproduction and Embryology (ESHRE) meeting in Turkey.