Mehmet Oz, M.D., is host of “The Dr. Oz Show,” and Mike Roizen, M.D., is Chief Wellness Officer and Chair of Wellness Institute at Cleveland Clinic. Email questions to youdocsdaily@sharecare.com.

QUESTION: My sister is having a baby (yes, we read your book “YOU: Having a Baby”), but she hasn’t taken the info in the book to heart, and she’s gaining a lot of weight.

She was a big girl to start with. I told her to watch her weight for the unborn child’s sake. What would you tell her?

— Sandra F., Manchester, N.H.

ANSWER: If you’ve already read our book, you both should be aware her health and the health of her yet-to-be-born are affected by her health and lifestyle choices before and during pregnancy.

She should know that she’s eating for 1.1 people, not two, and she needs just 10 percent more calories, not 100 percent more. Being overweight while pregnant can cause neural-tube defects in the fetus that impair development of the brain and spine. It can also cause elevated blood glucose in the mother, and that can trigger other problems.

Recent research shows when the mom-to-be has prediabetes, gestational diabetes or Type 1 or 2 diabetes, the signaling pathways in the fetus’ developing heart may be altered or interrupted. The result is congenital heart disease, the leading cause of infant death.

Exactly what issues develop depends on the amount of the pregnant woman’s weight gain and the degree of elevated blood glucose that happens in each trimester. Overall, the risk of congenital heart disease is increased four or five times.

Overweight moms-to-be also threaten their own health with preeclampsia, high blood pressure and kidney and liver complications. Delivery also may be complicated. The baby may be born oversized, making a C-section necessary (tough on mom and baby’s gut biome). The child may then develop weight, learning and speech problems down the road.

So, the smart step for your sister (and any pregnant, overweight woman) is to work with a nutritionist and exercise specialist recommended by her obstetrician. Following a healthy routine will help her and her baby have a healthy and happy life together.