DEAR DR. DONOHUE: Except for an increase in blood pressure, my pregnancy was uneventful, and my daughter was born healthy. I was given garlic to combat the high blood pressure. I stopped taking it about a week before my baby was born.

My labor was normal. But after the birth of my baby, I began to hemorrhage. To stop the bleeding, bimanual compression was done. My doctor said that postpartum hemorrhage is unusual, unpredictable and not preventable. My midwives blamed it on the garlic I took. They said it prevented my blood from clotting. Other doctors don’t think the garlic had anything to do with it.

What causes postpartum hemorrhage? Do you think garlic was involved? Will it happen again? – S.B.

ANSWER: In a routine delivery, less than 500 ml (about one pint) of blood is lost. Greater amounts are called postpartum hemorrhage.

It happens in about four out of every 100 deliveries, and the usual reason is a failure of the uterine muscle to contract as it normally does after the baby passes out of it. A uterus that is overly distended during pregnancy is apt to lose its contractility and lead to postpartum hemorrhage. Multiple births are another cause. Uterine fibroids can also lead to such bleeding. If pieces of placenta remain in the uterus, they can promote excessive blood loss. Women with blood-clotting disorders are, of course, subject to such a problem.

If no anatomic abnormality was discovered in your uterus that could promote bleeding and if you have no blood-clotting abnormality, then the chances of a second encounter with postpartum hemorrhage are not great.

Evidence for the claims that garlic can lower blood pressure, thin blood and reduce cholesterol is not great. I don’t believe it had anything to do with your postpartum hemorrhage. The fact that you had not taken it for a week before delivery makes it even less probable that it contributed to the bleeding.

DEAR DR. DONOHUE: What are hydrogenated oils and trans fats? Is there any safe level to ingest? – G.M.

ANSWER: Hydrogenation is the process by which hydrogen atoms are added to oils to turn them into trans fats. Trans fats, unlike oils, are solids at room temperature, and, unlike oils, they have a long shelf life. Furthermore, they add texture and taste to foods.

Trans fats increase blood levels of cholesterol. It would be good to avoid them altogether. That is impossible. It is possible to limit the amount eaten. Keep trans-fat calories to less than 1 percent of your total daily calories. Say you eat 2,000 calories a day. You should get only 20 calories from trans fats. That’s about 2.2 grams – a very small amount.

DEAR DR. DONOHUE: I am confused regarding the T score. In my hip, the score is -1.9, but in my back it is -1.5. What does all this mean? And what is the Z score? – J.R.

ANSWER: T and Z scores are numbers obtained in tests that measure bone density – a measurement of osteoporosis.

A normal T score is one that is -1 or higher. A score between -1 and -2.5 is osteopenia, a condition that indicates a person is on the brink of osteoporosis. A score of -2.5 or lower is indicative of osteoporosis.

One common test for generating T scores is the DEXA test – dual energy X-ray absorptiometry. The T score is derived by comparing a person’s bone density with the density of bones at their peak of health in young adults.

Test readings are taken in more than one bone. The hips, the lower back and the wrists are common sites. Bone density varies at different sites. The lowest reading is the one used to determine a person’s bone health. Your readings indicated osteopenia.

Z scores compare a person’s bone density with the density of healthy, age-matched controls. Z scores are not used as often as T scores. If you don’t mind, I won’t go into them at any greater length. I think it would serve only to confuse.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.