A new home test can tell expectant parents whether to go with pink or blue five weeks after conception, before the half-inch long embryo has even developed genitalia.

The Baby Gender Mentor test searches for Y, or male, chromosome DNA in a few drops of the mother’s blood. If it’s there, she must be carrying a boy. Otherwise, the baby is a girl, explained Sherry Bonelli, chief executive officer of pregnancystore.com.

The online retailer sells kits made by Acu-Gen Biolab, a Lowell, Mass., lab that performs the tests. The necessary blood sample can be collected at home.

Prenatal ultrasounds, usually done around the 18th week of gestation, are less accurate for sex identification because they are dependent on the skill of the technician and the doctor, as well as the baby’s position, she said.

Some insurers won’t cover an ultrasound unless the doctor says there’s a medical need for it, Bonelli said.

Tests such as chorionic villus sampling, or CVS, and amniocentesis also can examine the baby’s genes to determine sex. However, they are performed primarily in high-risk pregnancies that warrant the invasiveness and risk of the procedures.

Ethical concerns

In some countries, mothers have undergone genetic testing to find out the sex of their babies so they can then decide whether to continue or end the pregnancy, noted Dr. Allen Hogge, chairman of the obstetrics, gynecology and reproductive sciences department at the University of Pittsburgh School of Medicine.

The new test can provide that information more easily and earlier in pregnancy, making a first trimester abortion possible.

“That’s the major concern,” Hogge said. “We have no idea in this country whether people choose to terminate” based on the baby’s sex.

Bonelli is aware of the criticisms and ethical concerns.

“I don’t foresee it being misused as other people think it might be,” she said. “In other countries that might be more of an issue, but in this country I don’t think it’s going to be an issue.”

She added that here, “The majority of people . . . are going to use (the test) to find out the gender so they can plan ahead for their baby.”

Genetic screening

Scientists have known for several years that some fetal blood is present in the maternal circulation, allowing testing for specific genes.

For example, in Europe mothers who have an Rh-negative blood type are tested to see if their babies are Rh-positive. If so, the mother is treated to prevent an immune reaction against her child. But if the baby is negative, too, there is no need for further intervention, Hogge said.

“There are a number of publications about isolated genetic disorders that would be present only in the father and not in the mother,” he said. “Once the mother has it, you can’t detect what’s her versus what’s the baby.”

Some disorders, such as Duchenne muscular dystrophy, occur in boys because the gene abnormalities are on the X, or female, chromosome, of which males have only one copy. A gender test could ease worries if the baby is a girl, or indicate a need for further testing if it’s a boy.

However, “I’d spend (the money) on a genetic counseling session to find out what I was at risk for rather than finding out the sex of my child,” Hogge noted.

Also, if there is a risk of an inherited disease, parents should see a specialist.

“The Baby Gender Mentor isn’t meant for any type of diagnostic purposes,” Bonelli said. “They would go through their physician’s office for that type of test.”

Thank you, drive through

These days, most parents don’t want to wait nine months for a surprise.

“It’s estimated that 50 to 70 percent of expectant parents want to know the gender” of their baby, Bonelli said. “We’ve been overwhelmed with the amount of interest.”

One father-to-be spent extra money to have the blood sample couriered to the lab overnight, even though the kit includes a prepaid envelope that would get it there in one or two days.

“He e-mailed me back saying, ‘It’s a boy! We’re so excited,'” Bonelli said.