I lived in Bangkok for 4 years. During this time I was trying to conceive naturally and suffered 3 miscarriages. I did not try assisted reproduction although I was offered various options, ranging from artificial insemination to IVF. Therefore I do not have direct experience of IVF. My experience of the doctors and medical there in the private medical system was excellent however.
Overall the private medical care in Bangkok is of a very high standard. You probably have heard that medical tourism is huge in Thailand. The private hospitals are second to none in comfort, with accommodation and support services very similar to 5-star hotels. The Thai medical staff are highly trained; specialists train both in Thailand and in top universities, hospitals and clinics in the US, Europe and Australia. Medical equipment is brand new but efficiently used, hospital cases management is computerized and paperless. Costs are a lot cheaper than the rest of Asia (read HK & Singapore) but not India.
The major private hospitals for medical 'tourists' are:
Bumrungrad Hospital - this is owned by Bangkok Bank
Bangkok Nursing Home
Samitivej hospital
There are numerous other private hospitals that cater also for Thais and foreigners but none are as savvy (marketing wise) as the hospitals I list above.
All these hospitals have obstetric & gynae clinics, as well as fertility clinics.
I have heard of a fertility clinic, Jetanin
http://www.jetanin.com/whoweare/philos.htm that has a high success rate. The high success rate may be attributed to treatments that are experimental (eg gender selection as you mention) as there are no ethical rules or regulations in Thailand forbidding this. However I have no direct experience of this clinic so you have to make more inquiries of your own.