Let's examine Dr Cathy Baldwin Johnston's credentials shall we?

She is a family practitioner.  

Here is her bio:

 The American Academy of Family Physicians has named Cathy Baldwin-Johnson, a R/UOP and WRITE ALASKA preceptor and a 1980 graduate of the UW School of Medicine, the 2002 Family Physician of the Year. The national award was presented this week at the Academy’s Congress of Delegates in Atlanta.

Baldwin-Johnson, who practices in Wasilla, Alaska, has been a UW clinical instructor since 1987. She has been a preceptor for several medical students in the Rural/Underserved Opportunities Program. From January to June of this year, she was one of the preceptors for Wasilla’s first WWAMI Rural Integrated Training Experience (WRITE) student.

After completing her residency training in the Swedish Family Medicine program, she returned to her home state of Alaska, where she has now practiced for more than 17 years. She founded and serves as volunteer medical director for The Children’s Place, an advocacy center for abused or neglected children. In addition, she holds a position with the Alaska Statewide Children’s Advocacy Center Working Group. She also serves on Alaska’s Matanasku-Susitna Valley Sexual Assault Response Team.
Baldwin-Johnson received the Alaska First Lady’s Award for outstanding volunteerism in 1999. The Alaska Academy of Family Practice selected her as the 2001 Alaska Family Physician of the Year. She practices at Providence Matanuska Health Care.

Nothing in there about being a high-risk obstetrician.

From the AAFP website:

 Provision of cesarean delivery by well trained family physicians augments services available to women, in some places providing additional options for care, and in other places providing a service that would not otherwise be available. Regardless of specialty, there should be shared common standards of perinatal care. Quality patient care requires that all physicians practice within their ability as determined by training, experience, and current competence.³ Given that many family physicians currently perform cesarean deliveries and many continue to be trained for this service, it is important that there be a common understanding of the place for cesarean delivery as part of a family physician’s scope of practice and as part of the health care delivery system.
This document should serve as a resource for family physicians who are training for and planning to include cesarean delivery in their practice. It also will assist hospital and health plan credentialing committee members and administrators, obstetricians, midwives, nurses, and other clinical staff to understand the role of family physicians in providing cesarean delivery in their practice of medicine.

Does CBJ have that document?

Also concerning Downs Syndrome:

 Down syndrome (trisomy 21) is the most commonly recognized genetic cause of mental retardation. The risk of trisomy 21 is directly related to maternal age. All forms of prenatal testing for Down syndrome must be voluntary. A nondirective approach should be used when presenting patients with options for prenatal screening and diagnostic testing. Patients who will be 35 years or older on their due date should be offered chorionic villus sampling or second-trimester amniocentesis. Women younger than 35 years should be offered maternal serum screening at 16 to 18 weeks of gestation. The maternal serum markers used to screen for trisomy 21 are alpha-fetoprotein, unconjugated estriol and human chorionic gonadotropin. The use of ultrasound to estimate gestational age improves the sensitivity and specificity of maternal serum screening.

Did CBJ do this? 

From the Anchorage Daily News:

Early Thursday (April 17)—she thinks it was around 4 a.m. Texas time—she consulted with her doctor, family physician Cathy Baldwin-Johnson, who is based in the Valley and has delivered lots of babies, including Piper, Palin’s 7-year-old. Palin said she felt fine but had leaked amniotic fluid and also felt some contractions that seemed different from the false labor she had been having for months.

Palin kept in close contact with Baldwin-Johnson. The contractions slowed to one or two an hour which is not active labor the doctor said.

I don’t think it was unreasonable for her to continue to travel back Baldwin-Johnson said.

Baldwin-Johnson said she had to induce labor and the baby didn’t come until 6:30 a.m. Friday.

According to the New York Times:
Around 4 a.m. on the day of her presentation, Mrs. Palin stirred in her hotel room to an unusual sensation. According to the Anchorage Daily News, she was leaking amniotic fluid. She woke her husband and called her doctor back home. Go ahead and give the speech said the doctor, Cathy Baldwin-Johnson, who declined to comment for this article.

According to Palin herself, in her autobiography Going Rogue while giving her speech in Texas approximately 11 hours after her membranes ruptured:
“More laughs, more contractions.” Pg. 193.

 IF CBJ is a high risk obstetrician she would have advised Sarah to get her ass to the hospital.  Why didn't she?

Why would she allow Sarah to take Trig to her office three days after being born?

 There are at least 39 obstetricians within 25 miles of Wasilla.  Sarah had her pick of any of them.  Why would she choose a Family Practitioner who specializes in counseling sex abuse victims?

There is also evidence that CBJ was not clocked in at the MATSU at the time of Trig's "delivery".