Dr. Greene's Answer
Nature is a fascinating interplay of cycles, large and small. A woman’s menstrual cycle is both poignant and beautiful. During a brief time beginning with the conception of a child, a woman’s cycle stops. Her focus turns inward, toward the developing baby, the birth, and then the glorious first months of a new life. The pause between your menstrual cycles underscores the uniqueness of this time. Your menstrual cycles themselves, and even the momentous pause between them, are vivid reminders of your fertility. Women certainly can become pregnant again before their periods resume, even if they are still nursing. Over 65% of nursing women are ovulating by the time their babies are 6 months old. If you become pregnant, you will usually first become aware of this by changes in the way you feel. You may notice yourself feeling decidedly more fatigued, perhaps accompanied by morning queasiness. A new phase of breast or nipple soreness may signal another pregnancy. Most women will notice some such changes.
A home pregnancy test is an excellent way to get an objective answer. These work by detecting in your urine a hormone (HCG) created by the new pregnancy. The test could turn positive as soon as a few days before the day your period would have come (usually 14 days following ovulation). Since you have no idea when this might be, take a test if you feel that you might be pregnant. HCG levels should be detectable within 17 days following intercourse that leads to conception. A negative test does not necessarily rule out a pregnancy, but a positive one indicates you are almost definitely pregnant. If it is negative, try testing again in a couple of weeks. In the meantime I would certainly take care of yourself as if you were pregnant.
Your next question about whether it is okay to continue nursing your infant during a subsequent pregnancy is a great one. The answer is somewhat controversial.
Globally, a new pregnancy is one of the most common reasons for weaning. Sometimes the baby will initiate weaning because the milk tastes different or is less plentiful. Sometimes the mother will decide to stop from fatigue, from nipple pain, or from fears about the effect of nursing on the new baby. Still, millions upon millions of women around the world do choose to continue nursing while pregnant.
Some people feel that if you do nurse while you are pregnant, you will somehow steal nutrients away from the baby forming inside of you, or your breast milk wouldn’t be an adequate source of nutrition for your older child. I disagree with this. Your body instinctively makes the forming baby a very important priority. Whatever nutrients you take in will be shunted directly to help this unborn baby grow. If you maintain adequate fluid intake and adequate nutrition, there will be plenty left over for your breast milk to be a rich source of nutrition. Moreover, your one-year-old should be getting so many other rich sources of nutrition at this age that she’ll do fine. I believe continued nursing can be a great experience, provided that Mom pays attention to her own body’s needs. It is the norm in many, many cultures today and in most cultures throughout history. The luxuries of formula, other sources of infant nutrition, and birth control are relatively recent inventions: in other societies women have had to nurse while pregnant, and have done just fine.
Rest assured that day by day it is safe and healthy to pay attention to what you and your child both want, and to let the interaction between you be your guide.