Dr. Kathryn Olsen is outstanding! Her office is next door to Saints Memorial but I am pretty sure she delivers at Lowell General. She used to be a doctor at WomanHealth but opened her own office.
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WomanHealth in Chelmsford is great as well, and they now deliver at Lowell General. I loved Dr. Galvin (male, 40-ish, maybe?), Dr. Michelle Cochran (same age estimate), and Dr. Bass (male, hmmm...sixties?). Dr. C was my doctor but I've seen the other two frequently; Dr. Bass actually delivered both of my children and I absolutely adored him! He is very kind, VERY knowledgeable, good sense of humor, and patient :) Come to think of it, that description covers all the physicians I recommended here!
http://www.womanhealth.net/
You can click on their doctors to see more about each one.
Hope this helps!!