Беременная женщина ждёт врача.

Because it is a full adjective in the feminine nominative singular form, and it agrees with женщина.

In Russian, adjectives change to match the noun they describe in:

• gender
• number
• case

Here:

• женщина is feminine
• singular
• nominative (the subject)

So the adjective must also be:

• feminine
• singular
• nominative

That gives беременная.

These are two different adjective forms used in two different ways.

• беременная = the full form, used before a noun:
  беременная женщина
• беременна = the short form, used as the predicate:
  Женщина беременна

So:

• беременная женщина = a pregnant woman
• Женщина беременна = The woman is pregnant

This is a very common Russian pattern with adjectives.

Because женщина is the subject of the sentence, so it is in the nominative case.

The sentence is built like this:

• Беременная женщина = the person doing the action
• ждёт = the action
• врача = the person being waited for

The dictionary form of женщина is already женщина, so nothing changes here.

Because the noun after ждать normally does not stay in the plain dictionary form.

With ждать, Russian often uses an object form that looks like genitive or accusative, depending on the noun and usage. For врач, the form used here is врача.

A useful thing to know is this:

For a masculine animate singular noun like врач,

• genitive singular = врача
• accusative singular = врача

So even if you discuss the construction in terms of genitive or accusative, the actual visible form is the same: врача.

The dictionary form is:

• врач = doctor

But in this sentence:

• ждёт врача

Ждёт is the 3rd person singular present tense of ждать.

Dictionary form:

• ждать = to wait / to wait for / to expect

Present tense:

• я жду
• ты ждёшь
• он/она ждёт
• мы ждём
• вы ждёте
• они ждут

Here the subject is женщина, which is she, so Russian uses:

• она ждёт

Even though Russian uses the present tense form, in English it may be translated as either:

• waits
• is waiting depending on context.

The correct pronunciation here is ждёт, with ё.

In many Russian texts, especially informal ones, ё is often written as е, so you may see:

• ждет

But it is still pronounced:

• ждёт

So:

• written carefully: ждёт
• often printed casually: ждет
• pronunciation: roughly zhdyot

This is very common in Russian spelling.

A rough pronunciation guide is:

be-re-MEN-na-ya ZHEN-shchi-na zhdyot vra-CHA

Stress:

• береме́нная
• же́нщина
• ждёт
• врача́

A few notes:

• ж sounds like the s in measure
• щ in женщина is a soft shch sound
• ё in ждёт sounds like yo
• the final stress in врача́ is important

No. Russian word order is fairly flexible.

The sentence as given:

• Беременная женщина ждёт врача.

is a neutral way to say it.

But Russian can move words around for emphasis, for example:

• Врача ждёт беременная женщина.
  This puts more focus on врача.
• Ждёт врача беременная женщина.
  This is less neutral and sounds more stylistic or context-driven.

Because Russian uses case endings, the roles of the words are clearer than they would be in English.

No. Russian has no articles.

So женщина can mean:

• a woman
• the woman

and врача can mean:

• a doctor
• the doctor

The exact meaning depends on context, not on a separate word like a or the.

So this sentence could be understood in English in slightly different ways depending on the situation.

Yes. In Russian, adjectives can sometimes be used like nouns when the meaning is obvious.

So беременная by itself can mean:

• a pregnant woman

For example:

• Беременная ждёт врача.

That is completely natural if the context is clear.

In your sentence, беременная женщина is simply more explicit.