Many studies show how sensitive a child in the womb is, many things cross over into the baby, being that mothers share a blood supply with the child. A teratogen, a factor that causes birth defects, can be anything from a drug like alcohol, an infection or even an x-ray. The fetus is very susceptible to a mother not taking care of herself. However more recent studies are showing more and more of a connection to drug use and child development.

One study that supports this theory was done at the University of Pennsylvania School of Medicine; this study although preformed on rats showed a correlation between cocaine use on father and a difficulty in forming new memories in male off spring. The study reported that male offspring of fathers that had ingested the drug for a period of time prior to conception had reduced synaptic plasticity in the hippocampus. The hippocampus is located in the medial temporal lobe of the brain. The hippocampus is responsible for long term memory and spatial navigation. Researchers conclude epigenetics play a role in this. Epigenetics is the study potential heritable gene expressions, these do not change the actual DNA sequence; a change in the phenotype, not a change in the genotype. Epigenetics caused changes in the son's brain causing D-serine levels to be lower. D-serine, which is an amino acid that regulates neuronal activities and can also be used in treatment of schizophrenia. As a supplement it is also linked with reducing cocaine dependence and increasing cognitive ability. When levels of D-serine were increased of the afflicted rats, their cognitive levels rose and memory increased. In another study on humans, sperm was experimented on with regards to "the two main active cannabinoids of the marijuana plant". The sperm was tested on 41 male participants. When the sperm was washed with the cannabinoids the sperm had a reduced mitochondrial oxygen consumption. While this does not show impacts of this drug on fetal development it shows that reproduction is impaired by what the father does with his body while conceiving.

A third study shows a correlation between fathers that are heavy smokers and spontaneous abortion. The sample size came from textile mills in Anhui, China. The women were all full time employees, 20 to 34 years of age, newly married and had permission to have a child, also they were not to be pregnant prior to enrollment of study. There were 526 participants in total, none of the women had ever smoked. All the women kept daily diaries and were interviewed; husbands were also interviewed separately. The study showed that the "the prevalence of total pregnancy losses (early pregnancy loss plus clinical spontaneous abortion) was consistently highest in each consecutive conception among the group whose husbands smoked heavily (suggesting that some pregnancies that ended in early pregnancy loss would not have ended in pregnancy loss otherwise)."

There is a lot more information on this study as well as the other studies mentioned above in the links. These are a few studies that indicate that the fathers health habits, while seemingly not as important, do play an important roll in conception and development of a prenatal child.